Hey, that’s incredible! I’m sorry the experience wasn’t what you wanted, but what you’re describing doesn’t necessarily sound like a bug.
After some player feedback, we updated the pack disclosures site to try to be a bit clearer on how packs work. Basically, the system is not designed to go through the progression for all Portraits within a rarity before landing on Coins–when converting from a Mercenary Card, it picks a straight random mercenary and then checks if there are any available Portraits to offer for that particular mercenary.