I haven't tried End Portal yet as I found this out on my new 1.17 hardcore world, but:
Whenever I go trough a nether portal I have to quit to title and log back on to my hardcore world because the world won't render whenever I exit a portal.
This happens both ways: either going to the nether (the nether won't load) or going to the overworld (the overworld won't load).
Either way I need to quit and log back on whenever I use the damn portals, and I frequently use portals on hardcore playthroughs.
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duplicates 1
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Thank you for your report!
We're tracking this issue in MC-227996, so this ticket is being resolved and linked as a duplicate.
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Sounds like MC-228220, which is caused by the use of mods, specifically OptiFine.