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All zero, AKA AZ, meaning reporting zero on all accounts, carries a scoring penalty. You're lucky it's only 7, most gets hit with 15-20. No worries though, as soon as you report a balance on one of your cards next cycle, you will get the 7 points back. The logic for the penalty is that your report looks like you're not using your cards at all to everyone else who is not the issuer of each card who obviously knows about your activities internally.
I strongly recommend that you use CK only for its reports and to ignore the scores altogether, VantageScore truly is meaningless other than creating confusion for new comers like you, if everyone follows this golden rule, the number of new threads on this forum would probably be cut by a third.
There is no AZ method, only AZEO (All Zero Except One) method, AZ is only used to describe that you messed up by allowing the "Except One" account to post $0. And yes, the penalty for AZ is immediate just as is the lifting of the penalty when you report a balance to "Except One" account on the next statement.
Don't stress out too much, if you keep reading and learning you will eventually see the big picture, you will then realize that these little scoring variations caused by UTI or AZEO (no AZEO) are just temporary conditions, mostly meaningless in the grand scheme of things. The most importantly thing is to always pay on time and never carry a balance (paying interest), good scores will follow.
Credit Karma is useful for its TU and EQ reports that are updated weekly. Blow off the rest of it.
$5 is a good balance to report. You don't want to go much lower than that because most banks will waive small balances rather than bill you. When that happens, a balance of zero is reported. Small balance waiver thresholds actually vary from bank to bank and are almost always less than $5. But sticking to the $5 minimum is easier than keeping track of what each bank does.
(If you happen to have Bank of America's Better Balance Rewards card, let your statement cut at at least $10. They've been known to waive $5 balances. When that happens, customers lose out on their quarterly rewards.)
All my balances on my CCs just reported $0 today. I lost EX:-9, EQ:-20, TU: -1.
I'll get that back in 2 or 3 days when my other credit card reports with a small balance. I rotate the card that I let report every few months and because their report date is a few days apart, I either see all my balances zero'ing out or 2 cards reporting a balance in that tiny interval. So I can say with confidence, you need a card reporting a balance, though a small balance is better than a large one. If you don't have a lot of cards, then you don't want more than 1 reporting a balance. It doesn't cost you any interest to allow a card to report a balance. It only costs you if you don't pay the full balance from your last statement before the due date.
Chase FU will report a zero balance to CRAs within a day or two of payment. I know, I accidentally let it report zero ( due to a credit) mid cycle and I lost points like you did. Easy to fix, hate the wait.
CK helped me a lot also. I now understand FICO & credit much better. But, as you say, CK serves a purpose. Also... they are great to get alerts if something is going on with your credit. My Vantage3 scores steadilly rose on CK/CS. I loved controlling my credit destiny. As you are finding out, whats good for FICO isn't always good for Vantage3. My FICO scores now rise, my Vantage, not so much... they are now 30+ points lower than FICO.
I've seen a lot of posts from people saying they got Amex BCE with a score like yours. Maybe Discover also... hopefully others can help with that. You are on the right track. Scores go up and down... but... you are headed in the right direction.