$_SESSION variables not working

I am working on a website developed in PHP to run on a Linux Apache server. After some recent changes my session variables seem to have gone haywire. One of my pages creates a new session and then logs the value of the $_SESSION array using var_dump. Here's the result:

[25-Jun-2021 11:53:00.220 BST 1] on ,  L_TRACE Session ID = 500qbjglhu2vsvupfp5810kmi1, $_SESSION = {"54b4368deba7f09e24d876746ae2b9db3923d76b45e772c946201c80d3b23a289c629d230a0e5493e91a048b1532df4e76cb12ffce6d065e38179519f8f067e9":{"form_security_tokens":{"account_update":{"20210624":[]},
"permalink":{"20210624":{"20210624xM1EM0WHHtO5uMOLzhdWZXl_1yiPnbaw":true, "20210624M9lPBD1YzVXM8KLaM7rwJnkDg9FtzA5f":true, "202106243aJlw_Iy5aYa4CNKcL_Q3MAfWETrYTbv":true,
"20210624PYuE8WhOh11hhby1dWNF_u1T-vUGpybi":true, "20210624_SY8MAmGOE0fqTtaXqCl5fXt4YD9sZZA":true, "20210624YjJitJu-d8mxi2Or7UyPqhlOiBE73kOT":true}},
"manage_proj_update":{"20210624":{"20210624nxz7AccWkafXoNDLOotIzKA2vm9mV6zX":true, "20210624HJk2mTiaA8uWPPrShgfpCDqY86wR4o4L":true, "202106246TiBXRhlFl1vkU_FMXbwTJr5ThV5z0S5":true,
"20210624rFq5H-wyklXbjCTY53qyoof4m_-Z44ti":true}}, "manage_proj_subproj_add":{"20210624":{"20210624efF-zupy7wW5GEJlZEI2gJAKYHtFynWL":true, "20210624ULLEQoUf1J10BUGJL259P1v-2fG20tZ-":true,
"20210624ZDAuSPp9iFSQTifA0oMLkiJEcDvrUbzI":true, "20210624vzS-75bWzKN2JcFLr4GhOwxBV1iwcX2O":true}}, "manage_proj_cat_copy":{"20210624":{"20210624nxfXyJ4QUyXHgkfozskEJO6EP6YHxp2_":true,
"20210624n7ii3c8YZGfdmH5j_NFigU9tPQbG_tVf":true, "20210624QWQmc1ZS6YGe1GnP1u1gOpmAeaYGQNyY":true, "20210624fMn693XyPFPjO5fcrlpsIgWBtiAZhQSX":true}},
"manage_proj_cat_add":{"20210624":{"20210624iOBTNfEg2p56U2Gh6bPPftTh-OndKWBm":true, "20210624o_oFXFi99uPSYWCyHcgNt-UWpbZuRhlL":true, "20210624xa7mW24mM3WI_bzBi_A3ZgJrY31w0pQA":true,
"20210624Kye9oOZtNs6IgtGaOOh58bl6cIjsE-5V":true}}, "manage_proj_ver_copy":{"20210624":{"20210624yCtwU9Eh_Q8evhj0agL2ALBX-Kdq9Y15":true, "20210624G2twCmp8OWYxAc4S6h03wsgBxdSBiaX3":true,
"20210624zk6avEJ39U0Y9Wa7kjNISNEDsmpKurCg":true, "20210624qiAANl5kjuWRaJE5_1sZ7_YZLdX14gTQ":true}}, "manage_proj_ver_add":{"20210624":{"20210624-nqc6IAVlEUacFTAUuIrq6CWefCk9CX0":true,
"20210624ijNhHiwoCkXRGz4nrrlftV0-N5ftdCN3":true, "20210624def0dPDX29RFgnLtARuvTTcN1Yfg5g8w":true, "20210624c5YBW8bEMwaeWojPW2Ld4oVeILvJ2kGY":true}},
"manage_proj_custom_field_copy":{"20210624":{"20210624uAj2gYaBAjf44O9B2z3FSDZuyaaxlrPX":true, "202106244bRi43zT77-iuuYbsnkWTEgD0Pp__tH_":true, "20210624ELSRig10sRK6oZQZQ5j4uY4zW5GPFa15":true,
"20210624Jkb9NwmjtUHF_QH9jId6OZpDlmsQR_Tx":true}}, "manage_proj_custom_field_update":{"20210624":{"20210624uy1f1wWNDxjAASnF_jpfr8HF8S2gtJqZ":true, "202106249RiEAPxF8vnRddfZuE1hpRLXxWQnxgD6":true}},
"manage_proj_custom_field_remove":{"20210624":{"20210624KPTOfkBgo6i9_a3BODrkQFWuCfnU2tmr":true, "20210624tjEFBSAbgYU-YIdW5e2zG1VEpPLYKMKl":true}},
"manage_proj_user_copy":{"20210624":{"20210624oq7p3wPpURu3pV8P7A4pU597B6meZscQ":true, "20210624Hl_UI17X9v67dtx0y65EeOX6MnPAqLHp":true, "20210624IoawzezIskw_akl379LRb287c4daJI91":true,
"20210624-0Un7BjcjUux-jXAtsQER14uHWUf-4Qm":true}}, "manage_proj_user_update":{"20210624":{"20210624wOW4WAlBbmdtXTIk4eSbRe86jzEqaLxs":true, "20210624PyMu5HrLnMv4kPZCn9V6kMdfLSyrEGTE":true,
"20210624NLbcLX1lLr7BGbtsoTDrAkpfnvMkxqUd":true, "20210624Sooy5j82uBSPT3zJhpkQlizQ59r86qlX":true}}, "manage_proj_user_remove":{"20210624":{"20210624EmCq8cpyWkaDc3t8oHybALHC3GHFiB7K":true,
"2021062498fm0EQhCh3Pk2UqBOgbdFLDz1xPuPDF":true, "20210624Nx3_Q8iQbS9ir5mBIRLd135ebsAb3Bh7":true, "20210624JYOgd9KsHTbdapnZjqMJ4WqbK1XJ8Pw2":true}},
"manage_proj_user_add":{"20210624":{"20210624hdZgCQ5e7zV3klU63iptitW_UVNDEjbq":true, "20210624XJFXAa3_t8_dY-cAEZDCY9hG7U7VFdae":true, "20210624sueykQeNx3TLvNQtMUX_vhq2_1eMR8fw":true,
"20210624Vm2b_KeiuKt8c6fh-DtG0_h6hAhAuj1Q":true}}, "manage_proj_custom_field_add_existing":{"20210624":{"20210624Zfs_GoBBDr-8AW0Co_6uEdCKMqskaTkm":true,
"20210624BGzAgv0Pk8XRHCZXCkyRf44gTHGBLA_9":true}}, "bug_report":{"20210624":{"202106244ipSFZyEUEhbs3uqXmSsdF0G-2uppMm7":true}, "20210625":{"202106255ggFqd94_Pbw7xpkNXABmuOGRbaJhqf4":true}},
"bug_update_page":{"20210624":{"20210624V6io-MDvUK9ssjsrHPWQ78SFrQkXwlhc":true, "20210624f7Yi784qQbphDLqrXWtzws73au65zvbl":true, "20210624osexaQETKElgGMRKKlUM7xgQgGUVpFXp":true,
"20210624MCQiRMhDwdAiqfS8Lp-VmSJcs5Vjy4Oc":true}}, "bug_update":{"20210624":{"20210624lrqPrbU_ol0GvDMYqe83qKlvhaq19yEo":true, "20210624el-3pG7G5wgrqexRuD3q70eYJBYLq4nS":true,
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"20210624sWqPsELaRzM3Hby9AZ8TX7BZlEcOE2qn":true, "20210624b-MN0VDt3Oi3ncMW5NYbfga_xP7OuFMI":true, "20210624V1NeI5FmUhrRpE7E8WhYZhdRr0ECbHrq":true}},
"bug_stick":{"20210624":{"20210624Dt3vMbXHZ4P5s70aRfFQv4LILeCKZXiw":true, "20210624jROSXzGJvkJaV6RNJAFiVbS3QZu0Q2Yf":true, "202106240PBIELMS28-DJ3nH9bolbKdOsEd4PI60":true,
"20210624jDRjAPEWXJsYBk7naHodkUff4UsNOuC0":true}}, "bug_report_page":{"20210624":{"20210624tb3bzzh0B90ukvVAXi3pmTNg-uTZQCvv":true, "202106246RGK405w--iYtnkJ-bfXQSBPaXrgU1sT":true,
"20210624pvMrPbu5INJjmbyYOdoqpBAaJkVwQ4gB":true, "20210624OieySVVvkZytQNNt30ivajxNclMDG13i":true}}, "bug_change_status_page":{"20210624":{"20210624rNJ-tZn4goMIqCMgAp333hAD-tM0o68Z":true,
"20210624ijZ_0iYWUuiSRZRpLYWja0hJ3RZK0OUu":true, "20210624AYyZiAa3xA17ShMBuTeyH_dR--IhBFRQ":true, "202106245tNsaVnOc9QrxsvFk3NOtIX00xu-PV-4":true}},
"bug_actiongroup_page":{"20210624":{"20210624PyA-5OyEh9VODubuE3p_uvluA5sTRj0s":true, "20210624vTDVOpfTxCL9I5QMkPI4KQeELAdKYLQZ":true, "20210624c0ndZml_Hqtm99g4TuZjVH5SqqGbMCjd":true,
"202106243Wt_k4Wk_ZJUYS8VA_Be3btlobFfktke":true, "20210624wNXldn4Rck7QE-TMmuLzoZJuMkJx6NcF":true, "20210624-py2FfN9-4I5QybdVUYSkTJLk7QyqP9-":true, "20210624_ROPaWmy6L_re-zjix-1wxAUphG-kMmO":true,
"20210624i9pdsVeviWKGxHSSsNNeM1qKre9udoXu":true}}, "tag_attach":{"20210624":{"20210624tI2mfeoH_XeYVcMB32_QVBuil6gljbU3":true, "20210624EHQKRf1j-PcCARkrNCuOJpvloMMPoRK0":true,
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"20210624Fw5awNOs4F6chraP5eyXy95eWfWa2PLp":true, "20210624Vq6E57QFC0WNGaZbueVHc12s9Uz_tLbV":true, "20210624h92EOfUaAROkEkGKNaTr5b0uI6yiVKVZ":true}},
"bug_file_delete":{"20210624":{"20210624-FGHy5pbXqb11QhSlD-EVHUuH1itzTHq":true}}, "file_show_inline":{"20210624":{"20210624os6ny6dHn8D5YyI0g4wjbvdL_K7uM8HD":true}},
"bugnote_add":{"20210624":{"20210624224tdorca79kVrjJV994cRGisjiG5Eai":true, "20210624nBY25_0lRLJkqI3m9FskiwcyLTJk0vCL":true}},
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"bugnote_set_view_state":{"20210624":{"20210624dlTy4NyaWMGwEQiLa5Vn612Ht12UNv5l":true, "20210624mBoeiw49ik4xuSFA7dF8z0PPAmuYHAaw":true}}}, "secure_session":false},
"session_id":"500qbjglhu2vsvupfp5810kmi1", "lasttouch":1624618379, "breadcrumbs":[{"shortname":"Login", "filename":"index.php"}, {"shortname":"EditMember", "filename":"edit_member.php"}],
"request_index":53, "test_mode":0, "current_role":"1", "username_entered":"test.member", "login_member":null, "login_name":"Test Member", "auth_level":3, "Redirected":true,
"redirect_time":1624618379.964, "edit_member_mode":"new_password", "edit_memberid":"136", "formdata":{"MemberId":"136", "FirstName":"Test", "LastName":"Member", "ChoirNum":"0",
"Username":"test.member", "PasswordHash":"$2y$10$kicyiCZTVCjUUy8G\/6fJ2.BokRlOUVwCK6NJP60lE2xKGkKeOJhtG", "Email":"test.member@sylvesterbradley.org", "Address1":"", "Address2":"", "Town":"",
"County":"", "Postcode":"", "Phone":"", "Mobile":"", "Student":"0", "DivisionAbbrev":"B2", "SectionId":"1", "Birthday":943920000, "Joined":943920000, "DefaultRole":"1", "MustChangePW":"0",
"LastChangedPW":1549535706, "PasswordStatus":"2", "CPKey":"8UhlbhWnJ74q3twnREPqyXLFlquqgAAo", "CPExpires":1624625572, "LastTouch":1549536507, "SendReminders":"0", "Status":"1", "ChangedBy":"4",
"ChangedOn":1493461887, "Enabled":"1", "Welcome":0, "OldPassword":"", "NewPassword":"", "ConfirmPassword":""}, "authenticated":"key", "pageerror":"There were errors in the data you entered. Please
correct them and try again.", "fielderrors":{"LastName":"You must provide a last name.", "Email":"You must supply a valid e-mail address.", "NewPassword":"If you wish to change your password,  please
enter your desired new password (twice). If you do <u>not<\/u> wish to change your password,  please leave both boxes empty."}} at line 805 in file: /home/sylvest/include/functions.php
    Called from my_session_start() at line 190 in file /home/sylvest/include/basic_init.php
    Called from require(/home/sylvest/include/basic_init.php) at line 135 in file /home/sylvest/public_html/swchoir/edit_member.php
 

The first variable with the cryptic name makes no sense to me. I am 99.9% certain that I am not creating this session variable. So what is creating it? Where is it coming from? Does it matter?

Thank you - Rowan