did you send to gmail/hotmail/icloud?

hotmail and icloud are very sensitive and if IP isn't reach a certain reputation(mail volume+age) it's easiser to land on spam even SPF/DKIM/DMARC are passed. But if the recipient interact with sender(mark as non spam, send a reply) then moving forward email send from that won't be flag as spam anymore. So their spam filtering is kind of weak and they used previous interaction as a signal.

gmail, on other hand is rock solid. They have their own false positive obviously but they are rock solid in term of not relying on IP reputation(or less). They are smarte and righfully land your legitimate email on inbox even an email come from a spammy IP.