NullReferenceException?

My server started getting these this morning. “NullReferenceException: Object reference not set to an instance of an object” It ended up being about 10 a second for an hour until the server crashed. When the server came back online we were missing 50k entities out of 129k. Its a modded server. I haven’t changed or added anything since Sunday. Can anyone shed some light on what could have caused this problem?

Thanks!