See the log snippet here:
https://mclo.gs/o8oSii4

This was reported to me by a user; this is in a locally shared singleplayer environment (using an e4mc fork), so it's probably related to/the same as #796 (which is using Essential)

It seems the initial error is caused by the Target Dummy mod, but then subsequent disconnects are caused by the ingredient condition.

Judging by the log message and my addon's usage, the subsequent disconnects might be related to using the tag ingredient condition and that tag evaluating empty (due to all of the contents being optional objects), but I can't seem to reproduce the crash myself.