Looks like this one missed the patch notes, sorry about that. To confirm, this is an intentional change.
What you're likely seeing is that 20mm HE is now unable to hurt tanks and AA can hurt medium tanks but only at the right angles.
We know that 20mm and AA were pretty dominant before hand and we wanted to shake things up. It could have been that we've gone too far with this change, but in that case we'll be watching your feedback and willing to act accordingly.