(NOTE: optifine's 1.17 preleases were being used although I am not sure how that would effect the game in that way) was riding down a mountain on a horse and a one block fall was able to kill my player and my horse which were both near full health. not sure how to recreate but the video provides context.
MC-228773
horse and player die of fall damage when riding off not fatal fall
Resolved
Invalid
0
I'm going to close this as invalid since Optifine's 1.17 pre-releases are known to be very buggy and have glitches that might have caused this (specifically, world not loading properly after using a portal).
If you experience this in vanilla, please create a new bug report.