It seems that's the case... I don't have any glitches, but some people experienced crashes, and they fixed it by replaying and completing the level. So it's unclear... try firing all the red units before reaching the checkpoint and only take the exact number of troops that are required. Oh, and after the checkpoint cutscene, go straight to the castle and don't touch or interact with anything along the way; there are scripts tied to the units there.
Thank you:D, I'll try that, as I had a lot of units there before reaching the castle.
