I have noticed when I use a triplanar texture and I adjust the input image high/low/brightness/contrast value, rendering on GPU gives some warnings in the log about triplanar only supporting bitmaps on GPU.
I have more details posted in the Modo forum: https://forums.chaosgroup.com/forum/v-ray-for-modo/v-ray-for-modo-beta/1033812-warnings-when-using-triplanar-on-gpu
Is the warning incorrect? Everything seems to be working as expected.