When replacing convoys, convoys will empty themselves, but they do not go to the depot when they are completely empty and instead continue to roam their paths.
once they are in replace mode, you cannot manually send them to depot either.
in general, go to depot button doesn't work - you have to manually insert the depot to the schedule
Thank you for hte reports - now fixed on the 10.x branch.
The fixed version, 10.13, has now been released.