I don’t know exactly what caused this. I think it happened after a sword swing that may have hit two enemies, or possibly the sword swinger crashed into an enemy after or during the swing. After the sword impact, one enemy was ragdolled into a building that was a ground level above, and another was thrown normally I think.
After the impact, one of the enemy units behaved strangely. It was invulnerable to all ranged fire. The graphics for the unit would glitch and the model would be shown on screen rapidly swinging around the map, not in the place the unit marker was, except when the enemy unit was doing something. When it was doing something, it looked like it was T-posing on its unit marker.
The only way to defeat the unit was by hitting it with more sword swings. Its predictions were accurate and selecting it to attack with ranged or sword worked correctly.
In the below screen, note the model to the right and the unit marker to the left.