So here is what HubSpot support has come back with. They indicated that they are seeing this for a number of MS subscribers and currently recommend that it may be due to exceeding the outbound spam filter sending limit and or the default sending limits for the account. Currently my outbound spam filter limit is and has been set at 5000 emails / day, of which I have never even come close to exceeding. Same goes for the sending limits set by MS. Sounds like at this point, HS does not really have a solution as it seems that the MS AI is flagging it as spam apart from any sending limit.
On the MS side, I am still waiting on a response.
Curious what others are using for a cold emailing solution?