Dude, now I'm wondering about the messages saying there is a secret passage.

Definitely a bug of some sort it’s not intentional..

Because sometimes developers use workarounds or make mistakes. Elden Ring is a big game and you can be certain that it wasn't always the most skilled and experienced developers working on every piece of the game. Don't mistake something as janky as this as intentional game design, especially when as I noted, the prime examples don't actually lead to anything unique, running counter to the constant purpose of fake walls in FromSoft games.

Edit: If you want the most likely scenario for what these are, odds are early on they were actually intentional fake walls. Someone who likely wasn't as familiar with the environment design was probably asked to change it into a normal wall, and instead of asking a question, took a bandaid approach and tried to make the wall durable beyond what any player would actually try to do to test a fake wall.

They may just be removed paths. On reddit they have found several more but many of them have no items in them. The fact they need so many hits makes me think the devs tried to save time and put up hidden walls with a lot of hits instead of changing the level because they didn't think anyone would keep trying after the first few hits.