Killed enderdragon and entities entering portal result in a crash.

I killed the enderdragon one time and then the game crashed. I presume from my searches and from what I am seeing it is because of the XP falling into the portal.

I loaded up my world again with the dragon being full health again and only one crystal left to destroy.

Before killing it a second time I tried to cover the portal with blocks so it doesnt happen again but they were removed once I killed it again. So the game has crashed again. But now a save was created right after the dragons death with the XP already falling down so when I load up the world it almost immediately crashes. I tried copy-pasting a command to kill all entities to prevent the XP from entering the portal but the time slot from loading of the world being finished to the crash is too short.

I have added the crash report in .txt file as an attachment.