First it was 552, then it bumped to 554, then down to 553. Now it's 556.
It makes perfectly sense. It depends on what payments methods Patrons use. Example. If I pay with Credit Card the processing fee takes a few days. Let's assume that you decide not to authorise the payment. It shows 'member' (you cannot access the page but technically you are still a member) for a few days until Mastercard or Visa withdraw the money. If I use Debit Card same process but shorter. It shows as member but the exact payment is not finalised. If it doesnt finalise then you lose the member. It's a number that fluctuates a lot. Paypal also has refund options. If payment goes through you can ask for a refund it within a certain time. Especially at the beginning of any months number fluctuates a lot.
There is also the possibility that someone joined and forgot about it. Payments are processed. It happens more than you think.
Patrons who cancelled in the previous month do not have access beyond the 1st of the month, however these patrons are not removed from your patron count and "Active" list until 12 midnight Pacific Time on the 3rd of each month. If you notice a sudden decrease in your patron count, it means that those cancelled patrons have been removed from your count.