1.21.1 Crash when Activation Range option active

[VOrlando520]

Describe the bug
A clear description of what the bug is.
Crashes every so often when activation range is active

Reproduce
Steps to reproduce the behavior:
Turn on and configure Activation Range
Let server run for a bit until it crashes

Expected behavior
A clear description of what you expected to happen.
Not Crash

Versions -Latest is not a version!
ServerCore: servercore-fabric-1.5.5+1.21.1
Minecraft: Fabric 1.21

Mod incompatibilities
List any installed mods you think might play a role in causing this bug.
ServerCore
Lithium perhaps?

crash-2025-02-28_04.16.48-server.txt

The attached crash report is the same one from the last 4-5 crashes with the same crash. Does not happen if I have Activation Range option turn off.

[VOrlando520]

Also aware had this issue on 1.20.1 but its gone between versions with less optimization mods and a slimmed down setup. It only happens when activation range is enabled so am at a bit of a loss.

[Wesley1808]

The crash report suggests that the list of players currently in a dimension was modified off-thread, then the server thread loops through it and runs into a crash (if timed just right).

But really nothing should be changing that per-world playerlist off-thread, as that's unsafe. I do know that activation range can't be doing that.