Can confirm in 1.20.4
This posture glitch stops working when I leave and rejoin the world, and it seems to eventually occur after just playing minecraft for ~20 minutes
I managed to reproduce it again in 1.20.3, yet I still have no idea why it occurs at all.
Can confirm in 1.20.2
It first occurred when I was playing normally in the snapshot and decided to see the new third person shielding position. It happened every time I blocked until I left and rejoined the world. To reproduce it, I tried doing things that change the arm movement before blocking like eating food and aiming with a bow, but I couldn't find a way to make it occur consistently or figure out out why it happens at all.
This seems to be fixed with the {teleport_duration} option in 1.20.2 pre 1
Can confirm in 1.20.1
updating to java 16 fixed it, had to download the Java SE developement kit instead
since this is only an issue on java edition and it works correctly on mobs, I don't think it is
I'd also like to add this is patched on bedrock edition
done
Can confirm in 1.21.3