So, sometimes when you shoot the shot doesn’t go, or it goes trough the enemy without damaging, happened more that 10 times today so I thing there can be a bug
Where did you shoot the enemy tanks? Shooting through its suspension won’t do anything, or if your round is very large caliber, it could overpen.
Always check the server replay and from thier end. The shot will go somewhere, but also, you may not have fired due to damage which is a common one.
Your graphics settings can also play against you in some cases, where you aren’t seeing what you hit in the middle.