I'm 39 years old and apparently still don't fully understand credit cards

Disclaimer: in my defense I religiously pay off balances each month, so paying interest is foreign unless I mess up.

So I messed up: I use online pay but enter them manually and fat fingered a date. Payoff was two days late, so I got hit with the fees and interest. Fine, my own fault, I accept it. Schedule the full payment.

Now, here's where I'm confused: my next statement has a higher interest payment than the prior one! Ok, I get that my 2 day late payment went to the fee and interest before the principal. But shouldn't I be paying at most the interest on the small chunk of principal left from the first statement, not all of it accumulated? The spending was nearly identical. What the hell am I not understanding here?