Could it be a difference in Go runtime? It's happened in 4/4 of the last games I played, one of which was here. I'm using the Go runtime from winget; I don't know if the version here on Itch.io uses the local Go install, or a self-contained one. It does generally take a while to show up; I fought a few dozen raiders before these latest two decided to glitch. Also they are a cavalry and a swordsmen, but that's probably not related. Those are very common units.
perhaps check for and delete units with zero HP each turn as a quick fix?