Underlying error is:
Query: INSERT INTO `user_register_track` (ur_user_id,ur_user_name,ur_user_id_referral,ur_user_name_referral,ur_from,ur_date) VALUES ('4641','xxxxxxx','0','','0','2019-03-22 04:20:43')
Error: 1146 Table 'wiki.user_register_track' doesn't exist (localhost)
Strongly suspect that one of the last few additions to the wiki (extensions like CookieWarning, UserAgreement, etc) broke it.
Various online guides say to run update.php routine from CLI, but hasn’t helped.
Might need to add that user_register_track table somehow manually.