Just moved from GT 6.17 to GTU 6.15.08 and RF to GU blocks (both carried over, and newly crafted) can be placed and oriented as expected; however trying to use one only drains (up to) 100K RF/t from the power source and plays a quickly repeating explosion sound without producing the expected GU output.

video of the Flux Motor (Invar) specifically
https://mega.nz/file/LEc0AbgB#-kaqfOuAlkdu9ndVk5AHI4f48Mlvh1biSYIjpK9O2Ik