Bump
I'm having this issue too, I even tried to reset my server, aside from the fact that doing that didn't even reset it (it cleared the installed plugins list in the minehut dashboard, but the jar's are still in my server files and the plugins are still active) and I'm still encountering the issue where my server randomly shuts off/crashes while others are on it, getting the same error you mentioned.
I only started encountering this issue recently, when unleashed was released, I have never had this issue before and it's affecting multiple servers of mine.