CUDA should be available. When did it become unavailable? After a PP update? or just by itself? Have you recently updated the GPU driver?
1- Try trashing preferences.
2- Try updating or rolling back GPU Driver.
3- share with us full specs of your system + what version of premiere you are using so we can better help you.
Premiere & media encoder is all up to date
System: gtx1080ti, i7 5820k, 64gb ram, ssd's
trans coding from anything to h.264
lots more info with lots of confused users and apparently confused adobe employees.
I have a gtx1080ti, I thought this would handle the h.264 encoding?
Nope. H.264 encoding is handled by the cpu with QuickSync enabled.
Dont think your cpu has QuickSync.