I'm pretty sure this setup was working at one point for us. I changed our builds a bit to reflect some operational changes and now the CI git branch trigger isn't working. I'm trying to get it so when a PR is merged into master it triggers the release build. I can trigger this build manually but not when submitting a PR to master from dev and then accepting the PR (on github).
Is anyone else having issues or know whats wrong?
Adding an answer so this more visible. @starain-MSFT comment was the solution.
I added a new build with the same trigger and it fixed the other one not getting triggered. Then deleted the new build I had added and everything is working.
Cloning my build definition didn't work, unfortunately, and neither did saving a trivial change to the build definition. Instead, I had to explicitly disable the CI trigger, save, then re-enable it and save it again. (Annoying, because I had to redefine all the rules.) But give it a try if the accepted answer doesn't do it for you.
I also wonder if adding a random branch to the triggering branches list, saving, then removing the random branch and saving again would work (and save you from having to redefine everything).