Hey, I had a server crash with the Dragon entity here is the crash report

Forge: forge-1.15.2-31.1.41.jar
Mods: ProgressiveBosses-2.1.4-mc1.15.2.jar

crash-2020-04-10_01.43.28-server.txt

I don't know if it was your mod that crashed, but I'm posting it here :)

sorry english is not my language

Did you spawn the ender dragon with commands?

Fixed via ef2471a