I'm using Windows 10, git version 2.19, and SourceTree 2.6.10 (although I've gone all the way to 3.06 and still have this issue.)
\We recently changed the host of our repositories to Azure DevOps/TFS.
In Sourcetree, I modified the repository path using "repository settings".
When I go to the Terminal window (the first time) and issue a "git pull", the Git Credential Manager (which I installed with git version 2.19) prompts me to log in in via my companies portal login. The pull then works. It works after that too, no repeated login required.
The Pull button however, prompts me for a username and password (which I have iteratively cleared by deleting the passwd and userhosts files from C:\Users\*mylogin*\AppData\Local\Atlassian\SourceTree.)
Whether I let it prompt me or not, the Pull button then fails with a bunch of these messages: "fatal: ArgumentException encountered. An item with the same key has already been added." And a few of these messages: "Authentication failed for 'https://dev.azure.com/zzzzzzzz/xxxxxxx/_git/MyRepo/'" I've used every combination of credentials I can think of (full email address, AD network username, etc.)
I have two other machines I develop on - a Server 2012 box and a Server 2016 box. These work fine! I followed the same steps outlined above, and Sourcetree doesn't prompt me for credentials.
My gut feel is that my Windows 10 Sourcetree is unaware that the Git Credential Manager has already authenticated me using a Personal Access Token that it has created/stored.
Tortoise Git works fine on this box; no authentication prompts.
In my SourceTree options, I've tried both settings of "Allow Sourcetree to manage my credentials via the Git Credential Manager". I've deleted all the "Git Saved Passwords" in the Authentication tab. (There is one there now, from my latest iteration of this.) I've deleted everything that seems extraneous from the WIndows Credential Manager - Generic set. (I've left the one that I think represents my valid git/Azure/TFS Personal Access Token.)
Any suggestions on what I might try next?