There is a bug which occurs when holding some entity in a leash which has another entity as a passenger, and entering a Stargate going to the nether. For example, connecting a leash to a goat with another goat as passenger. The error does produce a stack trace, but does not specify an exception, so it's kind of weird. The main contents of the error message is as follows:
Entity passenger must match, cannot add {Entity} as passenger of {Entity}

It's unknown whether the leash is the important bit, but it does not trigger, for example when teleporing a goat as passenger of a furnace minecart.

Produced on paper-1.19-34.jar

An example of the exception: