The SporeEntity spawning clones in its onRemovedFromWorld method causes a ConcurrentModificationException when entities are being stopTicking during chunk unloading. I have observed that this issue has been fixed in version 1.21.0, but the fix has not yet been backported to 1.20.1. Since 1.20.1 is still a very popular mod version, hope this fix can be applied to it as well.