Comment 37 for bug 1640297

Uninstalling the nvidia binary driver (367.57) and moving back to Nouveau "fixed" the problem for me. The reproducibility of this problem seems to dependent on the nvidia video card model, as I have another workstation with another nvidia card model and the other one had no issue with the boot prompt on newer kernel.

The boot prompt UI definitely changed between -31 and -57 and the video driver probably mess up. So I don't think it's the kernel itself but plymouth (? or whatever prompts for the FDE password) upgrade that happened around the same time.