I know it's a very similar issue to a previous one "never ending merge in progress".
We are experiencing the same issue. One of our branch, is now stuck in a merge, and we cannot perform any other actions on VSO.
Can you help?
Added a solution by Visual Studio Team · Mar 17 at 06:59 PM
This issue has been fixed on the service - pull request merges should be working normally. If you have a merge that's blocked or stuck, you can click the triple-dot menu (...) next to the "Complete" button and choose the "Restart merge" option to start a new merge job.
The root cause was an issue with the job agents that perform merges running out of disk space. We'll perform a full root-cause-analysis to understand how this slipped through our monitoring and take the appropriate steps to ensure this doesn't happen again.
Can't resolve conflicts on a pull request