I have a local network minecraft server that was running for the past few days just right. TPS was 20 and there were no problems.

An hour ago the server started closing when we summoned the Wither. 

It always gives java.lang.stackoverflowerror. I tried running the server on a different computer in case it was a hardware fault but still ingame tps never got above 3.

[21:10:32] [Server Watchdog/FATAL]: A single server tick took 60.24 seconds (should be max 0.05)
[21:10:32] [Server Watchdog/FATAL]: Considering it to be crashed, server will forcibly shutdown.

^^^^^^this never happened before

I included the 2 newest crash reports and debug report