@dinuruian I just watched the replay.
When you captured the barracks, some of your pikemen kept capturing the building, while your friend didnt do the same when recaptured.
Thats why you kept the control of the building and he didnt
And you say you were playing as Athens, right?
If the territory gained from the building you captured ends up touching your own territory, then it’s expected that it won’t decay (even without garrison). But if the building remained isolated (not connected to your territory) and it was ungarrisoned, then that would indeed be a bug.
Do you have the replay? It would be good if you could share it so we can check what happened.
If you don’t know where to find it, you can go to the replays window, identify the match, and at the bottom you’ll see a text box showing the exact file path.