Versions
WorldEdit version: 7.2.1 Bukkit-Official(7.2.1+299386a)
Platform version: Minecraft Server 1.16.4 Yatopia (paper fork)

Describe the bug
With java 15 when i try to copy something even little (70 blocks) the server crashes
https://pastebin.ubuntu.com/p/yTx2vbWpts/

To Reproduce

1. Use OpenJDK15 and Yatopia (or paper)
2. Copy a little thing (I copied a fountain)

Expected behavior
After some seconds 10/20 in the server console you will see the crash and after a minute the server will stop

Screenshots
I have no screenshots but these are the log of the console https://pastebin.ubuntu.com/p/yTx2vbWpts/

Additional context
^^^^

This is more likely due to Yatopia. Yatopia is known to be rather broken, WorldEdit works fine on Java 15.

Sorry, but if I use Java 11 and yatopia I can copy just fine... It seems strange to me that is a yatopia problem

Looking at that crash it seems unlikely to be a WorldEdit issue as it's just getting blocks. I would also agree that it's a Yatopia issue.