This has happened to me a handful of times, but only on the speed round. This may just be a problem for those games, but its possible normal games have this problem as well. After I research an upgrade for a unit (not the unit itself) I would go to produce the unit in a province with all the prerequisites. However, it wouldn't let me use it, as if I didn't research the unit at all or the province didn't meet the requirements. I went to other provinces, and the exact same thing. I made sure I had all of the materials (which I did) and tried again, but no dice. The only way I could fix it was by refreshing or reloading the game, after which it worked as normal.
It's not major; refreshing doesn't take too long. It's just the few times this has happened I freak out a bit, and this can be especially dangerous during wartime.
It's not major; refreshing doesn't take too long. It's just the few times this has happened I freak out a bit, and this can be especially dangerous during wartime.