Hello, before I explain it to you first, I want to let you know that I may not be able to speak properly because I am Korean. Recently, I caught a dragon on a Minecraft server with my friends and made an enderman farm, but suddenly when I catch a dragon, the portal that opens disappears and there is a crystal on the pillar, but I haven't seen the dragon.
So I can't get out of the end at the moment and I'm on the verge of having to delete the server. And I'm running the server on a feather client and it's vanilla.
Thank you for your report!
However, this issue is Invalid.
Your game, launcher or server is modified.
If you can reproduce the issue in a vanilla environment, please recreate the issue.
Any non-standard client/server/launcher build needs to be taken up with the appropriate team, not Mojang.
A world which had previously been opened with a modified client might be corrupted. Please try reproducing the issue in a newly generated world.
Any plugin issues need to be addressed to the creator of the plugin or resource pack.
If you have problems on large servers like Hypixel, please contact them first as they run modified server software.