When using fast-forward in battle for a prolonged period of time (in my case, 5+ minutes), units (both friendly and enemy) will appear as if they are still in fast forward mode when switching back to normal speed. Switching to Forward appears the same as Fast-forward. The only one that looks different is when switching to Slow motion. This used to be an issue for me in past Total War games but that was due to my hardware not being the best so the game needed a few seconds to re-adjust speed. But I do not believe it is a hardware problem this time.
Video shows the issue.
Image shows at the top left that my FPS is stable when it happens. In this case, it is at 68. Gyazo link is available to zoom in, in case the number is not clear.
EDIT: Just noticed that the tree move as if they were in fast-forward as well.
EDIT 2: Added DxDiag, modified, preferences, and replay. Further information - issue fixes itself after leaving it on regular speed for a few minutes.gyazo.com/1259af0501c2f94193f2bb443e57b903