Shells will bounce off moving vehicles, and generally more often it occurs the faster they are moving. This is a BF2 hit detection/netcode problem more then a FH2 problem, the shots are not registering correctly. The Crusader, Cromwell, Daimler, Puma are all notorious for doing it. Cromwell also has some issues in the area between the top tracks and hull start, that gap there likes to absorb or deflect shots.
To help this somewhat, aim for the middle section (slightly to the front due to shot delay) of a vehicle moving perpendicular to you, aiming for as flat a shot as possible. The wheels can also cause this problem because they are moving themselves and the impact point can be at a strange angle inside the wheel assemblies. Side turret on German tanksis the best, side hull on everything else I can think of.
Tiger in the wheels, because they are only 60mm there compared to 80 in the hull and turret.
Other notes:
In 2.4, just expect to need a second shot and plan for it, odds are you will.
Loss of power over range is much greater in 2.4 then previous releases, your shots will be noticeably weaker now at range then before.
Avoid hitting any applique armor like sandbags, track links, or those added armor plates on the side of the Sherman Vs and the like, they are all specifically coded to be thicker and not just astethic. Also, never hit a Sherman in the turret with anything, between the curvature and the armor, your wasting the shots compared to hitting the hull.