ah, so the 64 bit update didn't kill the infamous 'vilshanka bug' unfortunately
this ui bug has been around for some time and used to occur quite frequently on vilshanka (hence the moniker), but is sadly not limited to this map alone. usually you can regain control by clicking on or entering/exiting an ambient building, but even this won't work 100% of the time. plus, once you run out of empty garrisons that usually means tough luck.
sometimes wildly cycling through your units and giving random orders before switching back to the bugged one can also solve the issue at least temporarily, but afaik there's no universal fix.
iirc it has something to do with how the maps were ported into the game on relic's side, so there's likely not too much mapmakers can do to prevent it from happening, either.
Does it /only/ happen on imported maps?
Perhaps a solution (Though it would be time-consuming) would be just to remake the maps from scratch in Worldbuilder? There has to be SOMETHING linking the maps this bug is found on...