The Bug

Player's velocity isn't saved after relog.

Steps to reproduce:

1./fill -10 200 -10 10 200 10 stone

2./fill -10 102 490 10 102 510 stone

3.Equip an elytra.

4./tp @s 0 200 11.0 0 30 and switch to survival mode.

5.Double press space to start gliding(Don't move your mouse)

6.You will land on the stone platform at Z~500.

7.Do step 4 and 5 again but quit and relog in at Z~250.

8.See if you can land on the stone platform again.

Observed result:

Your velocity is reset after relog and you can't land on the platform.

Expected result:

Your velocity is not reset after relog and you can still land on the platform.

Notes:

Actually, this bug doesn't need an elytra to reproduce, it always happens, but using elytra makes it more evident.

Relates to MC-128008. (Might be the cause of MC-128008)