Well, I don't know how it used to work to have both a CNAME and CAA record on the same name (your DNS server should prevent it, I would think, since it doesn't make any sense), but there is at least one other recent time here of someone saying that it used to work for them until recently as well. There might have been an update on Let's Encrypt's side that ended up stopping that configuration from working anymore, but honestly I don't see how it ever would have worked. CNAME means "go look over there", saying "but also look here for one of the records" isn't a concept that DNS has.
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