DMARC quarantine and reject policy algorithm
Solution 1:
DMARC requires EITHER DKIM or SPF to pass AND be in alignment with the visible from domain to pass DMARC. Yes, ideally, both SPF and DKIM should pass as some things break DKIM while other things break SPF, but you can consistently pass DMARC with only DKIM or SPF passing AND in alignment.
So if DKIM has passed consistently AND is in alignment then that's passing DMARC. Search for the d= domain in the headers. Is it the visible from domain or, at least, a subdomain of the visible from domain?