AI MRLS does not fire when used together with a Support module. When a fire mission is called they go through the drills of setting up and they even radio in a confirmation of firing the ordnance... But no ordnance is being fired at all.
This works with ordinary artillery and mortars.
Set up a support requester/provider system with some MRLS, call in a fire mission and watch them 'fail'.
Physical arty don't work properly yet. MLRS got problems and the scorcher versions as well. You can call for 6 but get 3 for example. And if you place 3 arty and call for 6 shots you might get 3 and only shot from 2 of the 3 artys.
So yeah, there is problems with the module and physical arty.