Salesforce Emails failing DMARC/DKIM only for one domain

Has anyone witnessed salesforce emails failing dkim check for some o365 recipients? It is working fine for all domains except a single domain wherein the dkim seems to pass on the email gateway but fails on the O365 check with error signature did not match

It sounds like the gateway is modifying a header that was used to create the signature. It doesn’t make any sense to check DMARC after the network perimeter. If all email arrives at the O365 via a hosted spam filter, that is where DMARC should be checked. It doesnt need to be checked again after an internal relay.