365 transport rule woes

Having difficulties with 365 and since the account was created by a 3rd party we have to go through them for support. They haven't gotten back to me since submitting ticket this morning so hoping someone here has run into it. Users are getting certain messages dropped by a transport rule. Investigating it the Drop Event is as follows:

Reason: [{LED=550 4.3.2 QUEUE.TransportAgent; message deleted by transport agent};{MSG=};{FQDN=};{IP=};{LRT=}]

Googling leads me to believe it's EOP related but we don't have any rules configured that would do such a thing, and the malware protection is to email me a notification if it logs a potential threat. Anyone run into this monster?