[MCM-799] Hard Crash in Mutant Battle Arena when bosses + multiple mobs battling

Partner Rank: 1

Partner Team Reporting: Jigarbov Productions

Verification builds and Platforms: 1.13.0.10 Minecraft - Release_2983494 Win10 Took a lot longer, but it also crashed in 1.13.0.4

Summary: Hard Crash in Mutant Battle Arena when bosses + multiple mobs battling

Impact: Crashes in existing content is bad. Mutant Battle Arena is one of my more popular pieces and this will impact all players who have it.

Repro Steps

Open Mutant Battle Arena
Press button for "Battle Arena Mode"
tp to -32 76 -82
press the buttons to spawn all mobs
tp to -32 76 -39
press the buttons to spawn all mobs
tp to -52 76 -60
give yourself a button and place it on top of the block at -50 76 -60
press that button a few times
teleport to -13 76 -59
press the button to "Open gates and start the battle"

Observed Results: The monsters start fighting, everything seems fine. Then, without warning and randomly, the game will crash. There doesn't appear to be anything, in particular, causing it.

Expected Results: The game not crash, maybe show an assert, or something in the content log to share what's wrong. Basically anything other than crash.

Screenshots/Videos attached:

See attached video of it broken in 1.13.0.10

https://www.youtube.com/watch?v=owCQ4Z2fz3o&feature=youtu.be

Regression Builds: It was confirmed working in 1.12.0.28