I tried the 163 kernel again, and there actually is a difference that I didn't notice before.
On 162, monitor displays "no signal". I can't switch to tty.
On 163, I can switch to tty.
EDIT: Here are my logs when booting on 163 into tty.
Seems like the relevant part:
déc. 19 10:02:39 coriacea-1 /usr/lib64/gdm/gdm-x-session[729]: Fatal server error:
déc. 19 10:02:39 coriacea-1 /usr/lib64/gdm/gdm-x-session[729]: (EE) Cannot run in framebuffer mode. Please specify busIDs for all framebuffer devices