For this, people have called out gunner optics being a likely cause.
In a very recent game on seversk, I even had the chance to test it out and yup, gunner optics can create magic.
Scenario: Centurion MK1 with mk8 shot (190 mm flat, 140 mm 30 degrees) shooting VK 3002 on mantlet.
Shot to the right side of the mantlet (or shoot left side from my perspective): Clean penetration, kills turret crew bar gunner and destroys breech.
Tank is immobile, not moving, not adjusting turret, nothing. Same angle, same elevation everything onto the other side of the turret to clean things up.
No penetration.
Try again, no penetration.
Shoot the side without gunner sight and it’s a kill.
This explains a lot of times I died to fighting panthers with APDS and other guns that should shoot clean through the mantlet: the side with the gunner optic is cursed. Lesson: shoot the opticless side.
Edit: Also server desync seems to matter a lot.
I checked replay and it seems I aimed lower according to the server than where I had my own cursor.
Edit 2: It seems like a not uncommon problem.
You look like you’re aiming for X on your screen/local recording while the server-side recording says you’re aiming elsewhere.
This reddit post shows it happening:
https://www.reddit.com/r/Warthunder/comments/1cq3fqu/server_desync_making_you_miss_is_cool_ig/