I had an issue today with one of my testcases in RSAT. When running it manyally from the RSAT UI it worked but when trying to run it from a PowerShell script I got this error:

Failed to download or overwrite attachment files – Some files maybe in use.

For some reason the test case uploaded duplicate files to Azure DevOps. When I ran the test in RSAT it uses the local file generated from RSAT and everything worked but when I ran it from the console it downloaded the files from DevOps, got the duplicates and for some reason failed.

The solution was to permanently delete the test case from DevOps and resync it from BPM.

Beware that that will give it another ID which will change the order of the tests.