We're working on merging code between branches on a web app solution using Visual Studio 2022 connected to a TFS 2018 server. We have three branches in TFS: program_main, program_dev, and program_newdev.
When we originally tried to merge code from program_main to the dev branch, we ran into a lot of problems and it was decided to merge instead from dev to main. So for this purpose and to preserve both preexisting branches, a new branch called newdev was created - a copy of the main branch.
Next we used Source Control Explorer in VS 2022 as usual to begin merging the dev code by changeset - with many files requiring the merge tool to resolve conflicts - into the newdev branch. The first changeset was completed, and the newdev program built and ran in VS 2022.
After merging the first changeset from the dev branch, the newdev branch was checked into TFS for purposes of functional testing, to make sure no changes were lost. The problem we now have is that we suddenly cannot merge from dev to newdev. When program_dev is selected as source and program_newdev is target, instead of seeing available changesets we now receive an error saying "No changes are eligible to merge from the source to the target".
Then we found an alternate method of trying to merge: Specific version -> Version type: Changeset -> Select source branch -> Find all changesets -> Select changeset -> Finish. The message after this method is "There were no changes to merge".
We have already done this merge process once but we cannot understand why it now refuses to work, or what to do about it. Guidance would be appreciated, thanks in advance.