Username can't entered / will automatically created

In one instance the username for new user can not be entered anymore. It says will be generated automatically.

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At the moment no external user-management (LDAP, via SQL etc.) is activated.

The point is few days before all act as normal. Which change could cause this issue?

Sounds nearly identically. I didn’t tried this add-in/settings, but the behavior is similar, i will set tomorrow the level to debug an try tomorrow some options of this kind, may i find the responsible one. Maybe some other add ins causes this behavior to. Thanks for that pointing out.