UPDATE: I just opened preferences to see if something changed, but it's still the same. but merely opening the preferences suddenly changed the GPU Compute
state in render settings to not being grayed out anymore and now cycles works again fast. what is going on?
ORIGINAL POST:
My cycles rendering is suddenly super slow... i didn't change anything in the settings. i was rendering for overnight then i noticed as it progressed it started getting slower and slower. so i restarted my PC. i was able to render each frame for just 1-2 minutes on 256 samples. suddenly it takes 15-30 minutes to render ANY frame even for 16 samples only. i checked my graphics card in device manager and it is still functioning correctly
CPU is at 100% and im not sure if that's normal even though it is supposedly using GPU. I have 32GB max memory.