this has only happened to me when i was upgrading buildings that would normally be required to retrain a lost troop. if i cant retrain a unit by normal means, then i only get one chance to retrain that unit. which is still a very good bug in the player’s favor, just weakened a bit since the update. if they fix this bug completely, you will lose even that one chance to retrain.
edit: tested and saw that this also happens if you have two airstrips and you are upgrading your second one, in which case it’s not as severe as losing that one chance to retrain at all, but more like losing that one chance to make retraining go faster. still, this is a good bug that just wasnt fixed completely and i wish tin soldier wont relay this to the team