[Rome 2] What could cause these graphic glitches?

These glitches as for now only show after a bit of time of playing, around something like 45-60 min. Graphics are set to low.
Since I play on a laptop with two graphic cards (AMD Radeon HD 8400 / R3 Series + 8600M Series), which is not optimal for a game so hardware intensive as Rome 2, at first I thought that they could be symptoms of overheating, with game files somehow failing to be properly loaded and rendered. However, considering also that Rome 2 is buggy and that AMD drivers gave me problems in the past for other reasons, these glitches could also be issues of driver compatibility and optimization.

Or it could be the Divide et Impera mod that needs to be updated, and perhaps this is probably the best bet, although I didn't find (yet) any reference about this mod giving such problems.

But I don't really know. Do you have any hint?

It might be your resolution - it looks non-standard.

These days Rome 2 is pretty stable - in fact I've personally not had any problems.