SourceTree fucked up my credentials?

I removed all saved credentials and wanted to add a new account/credential for my Gitlab server via Tools-> Options -> Authentication -> Accounts -> Add

I choose

Hosting Service: Gitlab CE
Host URL: https://<URL>
Preferred Protocol: HTTPS

Authentication: Personal Access Token
Username: <not available>

when I than click on Refresh Personal Access Token
SourceTree asks for Username and Password

I 100% sure to provide my login data but it claimes
Failed to ckeck login for user []
User Details check failed

The result now is that not only I can not access my repositories using SourceTree BUT I get a 403 - Forbidden page in any browser while the page is still available normal for other users. I tried to clear all caches, removed every entry for this server from the Windows Crendetial Manager and finally rebooted.

The issue still is here I can not reach my own server's page anymore from any browser on this PC!

Update

The issue was after a few attempts my IP was blocked by the gitlab server itself. I could solve this by removing the lock for my IP.

However the main issue still persists namely it is not possible to add a credential/ remote account for Gitlab manually.