Try toggling hardware acceleration.
Could it be madVR?
I dont think its MadVR as MadVR does not do video deciding.
Only problem in v2014 I cannot figure is 2160p59 (other probkems like 3D not working have weird solutions) ... as i mentioned, do software decoding with 2160p59 does not fill any madVR queues ... do hardware decoding fills queue but have "presentation glitches".
Updating motherboard bios and drivers, solved " presentation glitches" ... so hardware decoding works
But software decoding still cannot keep up for 2160p59 resulting in empty queue in MadVR ... lots of stuttering
Using software decoding on my machine:
1. 1080i59 uses 32% cpu
2. 1080p23 uses 24%
3. 2160p23 uses 63%
4. 2160p59 uses 100%
I believe LAV components is doing decoding ... this was not issue on 1909
... wonder if v2004 patch some security hole that resulted in CPU performance drop (pity i did not benchmark my PC before)
in short ... ppl who are into video ... i recommend not to upgrade to v2004 at the moment