The bug

If you have the nausea effect while going through a Nether portal will cancel out the animated portal overlay.

To reproduce

1. Give yourself the nausea effect

   /effect give @s nausea 1000 0

2. Switch to Survival mode
3. Enter a Nether portal
   → The portal teleport overlay doesn't show up

Code analysis

Code analysis by avoma can be found in this comment.