different set of active branches at the same time from the same vcs root in different builds

Hello!

A branch will be considered active if:
1) it is present on VCS side and had commits in, by default, last 7 days (as the VCS roots are matching, this is unlikely to be the cause of the issue)
or
2) it had a build in last 24 hours by default. 
The details may be found at https://www.jetbrains.com/help/teamcity/working-with-feature-branches.html#WorkingwithFeatureBranches-Activebranches

What is the branch which is considered active on one build configuration but not on the other? Any chance it has been started there either manually or via dependency/non-VCS trigger? 

Please also let me know if for either of the configurations these build parameters are present (they affect the above defaults, so if they are present active branches set may also differ):

teamcity.activeVcsBranch.age.days
teamcity.activeBuildBranch.age.hours

Thanks for the description of active branch.

Sorry, I didn't point out the real issue. The main problem about the differences is that one of the build is missing branches in one of the builds. (the branch was a new branch in the repo) but only some builds with the same VCS roots and same VCS trigger can see this branch. some can't. the behavior persisted.

Hello!

Could you please compare one build which lists a branch and one which does not by:
1) VCS root settings (e.g. they may have a modified copy of VCS root which will operate on the different settings)
2) build parameters? (in particular, if there are parameters I have shared before).

1. vcs root setting is exactly the same as both attach to the same VCS root belong to the root project.

2. default values for both properties

teamcity.activeVcsBranch.age.days
teamcity.activeBuildBranch.age.hours


further more, the missing branch in one of the builds is not in active branch, also not in inactive branch. just missing from the dropdown of branches available for the build.

Could you please reach out via Submit a request form above? This will allow you to attach files in a private manner; I would like to ask you to provide teamcity-vcs.log(s) from <TeamCity Server>/logs folder. Please also copy a link to this thread so your request will get routed to me.