Upon an entity getting stuck in the Ratlantis portal, it will be duplicated apparently, with the server console spamming the following messages:
[19:13:02] [Server thread/WARN] [minecraft/ServerWorld]: Trying to add entity with duplicated UUID fc9eb37e-c2b6-4c40-afc3-ced4ff81195a. Existing minecraft:arrow#169596, new: minecraft:arrow#217965
[19:13:02] [Server thread/WARN] [minecraft/ServerWorld]: Trying to add entity with duplicated UUID fc9eb37e-c2b6-4c40-afc3-ced4ff81195a. Existing minecraft:arrow#170213, new: minecraft:arrow#217966
[19:13:02] [Server thread/WARN] [minecraft/ServerWorld]: Trying to add entity with duplicated UUID fc9eb37e-c2b6-4c40-afc3-ced4ff81195a. Existing minecraft:arrow#169596, new: minecraft:arrow#217967
[19:13:02] [Server thread/WARN] [minecraft/ServerWorld]: Trying to add entity with duplicated UUID 108571f4-b610-45f5-83d1-586b7054baa8. Existing minecraft:item#169604, new: minecraft:item#217968

The current solution is to destroy the Ratlantis Portal with the stuck entities, which stops the console spam.

Of note: This can sometimes lead to the server crashing, with no crash report.

Fixed in 5e55839