Duplicate entry 'user__name' with Drupal account provisioning events

Problem/Motivation

I ran into some issues with the version 8.x-4.x in context with the "Drupal Account Provisioning Events" settings.

Situation:
- Drupal 9.0.9
- drupal/ldap dev-4.x

- No checkbox selected at "Drupal Account Provisioning Events"
- LDAP Query configured. Test of query works successfully
- If I run the ldap_user_cron() then the users are updated correctly

Issue 1
At "Drupal Account Provisioning Events" I check "Create or Sync to Drupal user on successful authentication with LDAP credentials" and run the cron again. I get the error Integrity constraint violation: 1062 Duplicate entry 'XXXXXX' for key 'user__name'
This occurrs, because GroupUserUpdateProcessor::runQuery() calls the method drupalUserLogsIn(), which then calls syncToDrupalAccount(), because of this Drupal account provisioning setting.

Issue 2
I get the same "duplicate entry" error, if I check the other checkbox "Create or Sync to Drupal user anytime a Drupal user account is created or updated."
In this case, saving the user causes the ldap_user_user_presave() hook to be called. Which calls drupalUserUpdate() and this again leads into calling syncToDrupalAccount(). Therefore, we run into the same issue.
In this case it also effects the user handling in other places. For instance, I can reproduce the error with this:

$users = $this->entityTypeManager->getStorage('user')->loadMultiple([10, 11]);
foreach ($users as $user) {
   $user->save();
}

If I check the logs afterwards, the error occurs while saving the second user.
Example:
- User 10, username "foo"
- User 11, username "bar"

User 10 updated successfully. While saving user 11, the error appears with the username of user 10, but with uid of user 11.
Duplicate entry 'foo' for key 'user__name' ...... [uid_placeholder] => 11