Same problem happen to me in both 1.5.8 and 1.5.9, the game doesn't crash, simply freezes (witch means no dump and no crash upload), CPU and RAM usage remains unchanged but no GPU usage.
"rgl_log_errors_xxx" logs nothing out of ordinary, remains the same as the game started, last one is "Build Version: xxxxx", and that's it.
I can almost reproduce it stably with a big battle (usually more than 1000 enemy troops and over 1200 both sides combine), and it always happen when there's around 20% (sometimes more sometimes less) of enemy's "power bar" left, and there are a lot of men fighting in the scene.
The issue seems to occur less likely when there are very few men in the scene, that's actually how I've been able to finish those big battles, just avoid looking at the "main battlefield", running around chasing a few men in some corner.