You don't utilize any https://docs.moodle.org/en/Authentication, only https://docs.moodle.org/en/Manual_accounts ?
You have Moodle 3.2, that means you haven't done anything, like Moodle upgrades, system upgrades for some time? When did the problem start? I mean the calendar date and any changes that have been done around this time.
Hardware and performance
Login from web and app take too much time
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