This is a clone of MC-111516. It is now indeed much harder to run into but its not fixed completely and you can still run into it in survival, without abusing commands.
Steps to Reproduce
Method 1: Using boat and blue ice
Create a superflat world covered in blue ice
Press F5 twice to enter front facing third person mode
Angle your camera towards the sky (press it into the ground)
Method 2: While falling
Press F5 twice to enter front facing third person mode
Run this command
/execute in minecraft:overworld run tp @s ~ ~1000 ~ 0 45
While falling, hold W and sprint
Method 3: Using elytra and riptide
(On a regular superflat world) give yourself an eltra and riptide 3 trident
Make it rain
Go into third person
Fly up into the sky at about a 45 degree angle
Once you hit the snow layer start aiming down at about a 45 degree angle
Method 4: Using experimental minecarts
Build a long looped track
Set
minecartMaxSpeed
to 100 or moreRide the loop
Go into third person
Observed Results
In all 4 cases you will observe your player model flickering
Expected Results
The player model wouldn't flicker
Attachments
Comments 8
That's because MC-111516 was always generally about high motion regardless of the vehicle. The report summary simply incorrectly implied it's elytra specific (because it was the most common scenario)
As such I don't think 1.21.3 should be in affected versions as this report is specifically about the issue persisting post MC-111516 fix so any version before the fix isn't relevant
Is the result seen after running this command in third person front and waiting around ten seconds the same?:
/tp @s ~ 2048 ~ -135 45
Can confirm.