A desync occurs when a player enters a Nether portal. I noticed this issue on Paper 1.17 where my player would momentarily appear at the wrong coordinates before correcting itself a split second later. This is not noticeable with higher ping.

Today, I saw the same issue but from a different POV. Another player returned from the Nether and on my screen, they spawned 3 chunks away from the portal. Their position did not quickly correct itself resulting in them appearing to phase through walls. 

I have confirmed that the bug is present in Vanilla with the default configuration, world spawn set to 0,0 and spawn radius set to 0. It seems to only occur near spawn.

The screenshot doesn't do it justice, but this is where they spawned on my screen (highlighted with a red box). They spawned a decent distance away from the portal.