Huh. That sounds like a bug actually! You can move units as many times as you want! Thanks for playing - gimme more feedback if you have any!
I only hope there are MORE units and twists added! If it happens again I'll try to give you any relevant info.
A potential clue, at least one of the times it happened, when highlighting the stuck unit, I was getting the unit info of another unit somewhere else on the board.
Can multiple units share the same space?