Why does my bullet only bounce horizontally or vertically, even when it's fired at an angle

As some follow-up questions, then ^{(Not necessarily that I need the answer to, but things to consider, more than anything else)}:

What shape(s) of collider(s) are you using on the bullets? Are the walls they're hitting square colliders? (If not, are they convex or concave?) Are they hitting the intersection of two adjacent wall panels? What physics material properties do they have? Are there any other adjustments made other than orientation correction in scripts?

There are numerous little possibilities that could have an influence on their interaction when left entirely to the physics engine. If the bullets are flying especially quickly, it could be a hiccup in resolving their new velocity. Even if not, it's easy to wind up with unexpected results.

It doesn't necessarily explain the results you demonstrated with the image, but without having experienced that behavior myself, I'm just trying to help think of as many possibilities as come to $$anonymous$$d. Of course, if anything stands out, just let us know!