@giuseppe87 I've replicated the Saving a user overrides the authname 🐛 Saving a user overrides the authname Needs review issue from 3.2. But I've found that patch #4 from that issue still works on 4.x-dev.
We use a custom Unique Identifier field and so we were running into this issue, where the authname would update in the authmap table each time the user was edited. On next login attempts, Drupal would create a new user prefixed with "simplesamlphp_auth_" and log an error:
Error on synchronizing name attribute for uid 12345: an account with the username johndoe and uid 123 already exists.
Seems related to https://www.drupal.org/project/simplesamlphp_auth/issues/3347716 💬 Module is auto-creating users prefixed with "simplesamlphp_auth_" Active
Patch #4 is so far working.