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If you have zero balances on everything, that is why your score dropped so drastically.
Make sure a small balance reports on your cc - somewhere from 1% to 9% of its individual limit in order to get your points back. I am assuming you are using FICO scores and not Experian scores directly from their site. For some reason FICO wants to see a small balance on one cc and not zero across the board.
You should really pull your 3B report here to get the variety of FICO scores: FICO 08, bankcard scores, mortgage scores and auto enhanced scores. That way you know the impact of paying off your auto loan. If you read through the site, you will see that many people get a hit for the payoff of their auto loan, but gradually begin to regain those points after a month or two.
Open a small ($300-$500) secured personal loan from your bank or CU. You are losing points mostly for credit mix, because now you only have revolving credit. Also consider opening a second Capital One account. That will get you to the recommended three bank cards.
I would suggest letting only the Cap One card report a balance of around 2% of its limit, rather than the no-limit Amex.
If your score dropped 4 pts from paying off the $5 balance on the one card, then get a $5 balance back on the card to raise your score back up the 4 pts, then you are above your needed number. I would strongly advise against opening any small loans at this time if you are planning on going for a mortgage soon, because initially it would drop your score even more.
It should be 9% or less of your Capital One credit limit.