What is your operating system?
What is your Shotcut version (see Help > About Shotcut)? Is it 32-bit?
Can you repeat the problem? If so, what are the steps?
I’m trying to save a preset using the hevc_nvenc encoder with the Constrained VBR rate control. When I go to save it, it reverts back to Constant Bitrate. It seems to be just this particular encoder that doesn’t save correctly as far as I’ve seen.