Hi, I lost my screenshot, but...
The AI can stack more than 8 units on a tile, resulting in a stack with no number on it. When I saw a stack with no number that was present more than one turn, I naturally prodded it with my hero (thinking it was a lone Devil). There were 13 enemy units. This pattern continued throughout my test of Final Stand, and can still be observed in that game. Tends to happen with large numbers of units owned by Black; trying to move past each other I guess?