SourceTree can't connect to git

[Balint Nagy]

I've been using sourcetree for about 2 years now, a year in the current environment.

Recently, it started asking for github credentials over and over again. At this moment, it doesn't connect at all.

I verified my credentials by logging on to github.com.

I checked the stored credentials in SourceTree under Tools/Options/Authentication. I tried to delete the stored ones - but I can't. I tried to edit the topmost one, but the problem remains.

Any ideas how to make it work?

Edit:
In Tool / Options / Authentication I have 3 different entries, all of them are marked as default - and I can't delete them.

[Balint Nagy]

Another issue might have been that my origins were using http:// urls (as opposed to https://).
I nuked my SourceTree settings (see https://confluence.atlassian.com/sourcetreekb/how-to-wipe-sourcetree-preferences-412484640.html although I found them in AppData\Local\Atlassian, not at the path mentioned in the article).
After restarting SourceTree I could clone github repos again, git communication seems OK now.