If you level up a military unit to max level, give it all the promotions, and get some more xp with it, it hits another promotion threshold, that it can't complete. This gives you a notification on the right side, for the promotion, luckily only one time, still, useless. The main issue is that the Automatic Exploration button becomes inactive with the red text Promotion available. So that unit can no longer auto-explore. I tried moving it to a city, in and out of friendly territory, having more combat, going in and out of water, nothing worked, still can't auto-explore.
This has been in the game since 2016 (found steam forum posts, but no reports about it here).
This has been in the game since 2016 (found steam forum posts, but no reports about it here).
