Just wondering if anyone has the same issue as I do: overall the game runs very well, I get constant ~60fps on highest settings, until I start a turn-based battle. Then, suddenly several issues occur:

1. The game starts to stutter, there are fps drops all the time,
2. The game freezes for half a second when one of my chars deliver a killing blow,
3. The most annoying thing for me - there is a very noticeable mouse lag for the duration of the turn-based battle.

I can live with 1 and 2, but the mouse lag is driving me insane. It's feels a bit like when you have vertical sync enabled in some games and it makes the mouse cursor feel sluggish. Again, this only affects turn-based battles - everywhere else mouse is working just like I would expect it to. Real time battles also don't have this problem.

Tried running the game with and without mods, on highest and lowest graphical settings, with different CPU affinity settings - nothing works...

I had the same problem and I think it had to do with some incompatibility with the controller plugin. Go to your Wrath installation location, open Wrath_data and from there go to Plugins, then x86_64, and in that folder rename the Rewired_DirectInput.dll file to Rewired_DirectInput.dll.old

Lower the polling rate of your mouse. Normally it's set to 1000 Hz and this is the highest setting. Newer devices can offer polling rate settings of up to 4000 Hz. In any case change it to the next lowest available value. From 1000 Hz to 500 Hz and if this doesn't fix it try 250 Hz or 125 Hz.

Since I don't know the model of your mouse you would have to look online for a guide how to change it for your device.

If this doesn't help check any software that's running in the background with capability to display overlays. NVIDIA Ansel, Galaxy even when its overlays are disabled, just shut it down completely and kill any related services via your Taskmanger, Steam, Windows 10 XBOX component/task/service, disable them. If they were causing the problem you can safely set your polling rate back to a higher value which normally shouldn't cause any input lag or stutter/freeze.

I've got a Razer Viper and played with the pooling rate - there was a change, but not for the better. Sadly, lowering the rate only added layer of stuttering on top of the sluggishness. As far as overlays go, I only had the Galaxy one - disabling it also didn't work :(

Already done :)

Since sadly the polling rate have done nothing the only other thing I would suggest you could try in the meantime is to deactivate G-Sync or Freesync, limiting your max fps to 1-max fps or a different lower value, turn on v-sync in your graphic card control panel and see whether this resolves the issue. As with the polling rate there's no guarantee for it to work but it's worth a try.

Oh! One last thing I read about while looking for a clue to help solve your issue is to calibrate your mouse. Seems to work for others who've experienced this same behavior though not necessarily in Wrath. In the end I guess you're a victim of Unity as well though less bad off as you can play the game where you'd most likely have to wait for the official patch.

One very last thing I forgot is to disable enhanced pointer precision and/or mouse smoothing. So now I think that's all I can come up with for you to try. All the other things I found really ... there's no reason to mess up half your system in order to resolve this issue when, as I mentioned, this is likely something Unity is causing.