Horses and other entities with big hitboxes often die by suffering in walls when going through normal size (3x2 portal block) Nether portals. This is very annoying on early state of world when you use horses to travel instead of using for example very expensive ice roads.
Also RIP all my horses that died in this way.
Thank you for your report!
We're actually already tracking this issue in MC-80032, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
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