Yeah, like mentioned the pattern in this game is, whenever someone jumps, block high then block low. Ideally though, you really should have some kind of reversal or push-block or something ready after blocking (or in some cases before blocking, so you avoid the situation altogether before it happens), you really want to avoid being on the defensive for too long.
You can avoid the mixups by chicken-blocking, but that opens you up to air throws, so you have to watch out for that. Another thing you can do is chicken-block the high then air-throw the opponent before they land (or high block into regular throw after they land).
Anti-airs can work too, but that’s very dependant on what character you have or what character you’re fighting against. Spidey can spider-sting to beat out most air attacks, Doom can use missles or sphere flame to hit anyone attacking from directly above (but not diagonally above like, say, where Vergil usually attacks from), Sent can jump straight up (or up-back) and j.M or j.H, then double jump forward or fly and do it again. Characters with a fast air dash and a good air normal like Doom and Storm can super jump straight up, wait for the opponent to be under them, then dash down while pressing a button (i.e. j.M for doom, j.S for storm).
There’s lots of options available, you just need to figure out where the character you’re fighting is most likely to attack from and what options you have available to you when they do that.