IF you can make more than a 360 deg move then there is no hard limit on A. It would not make any sense to have one. The theoreticle limit is like a zillion revs in each direction. WAY UP THERE. So I dought you have hit it.
One thing to remember when working with the A axis is SOMETIME you are going to have to unwind all the degrees you called for. Either by runing the code or refhome the axis to reset the machine A0.
In the old days you only had 0-360 degrees in a rotation and you had to account for that in code. Today you have it better with Mach3 letting you wind up the axis.
HOW do you have Mach setup for on the A is it 360deg or continous roll over?

Set up your machine then do a test. Refhome the A axis so the machine dro vlaue is Zero and then zero the work dro. Now the A is at machine home and work home.
Now from the MDI try a Gcode like G00 A 3600
The A should rapid around 10 times in the positive direction.
BUT even then if you are doing carving on a tube you should never go beyond 360 anyway(;-) (oldschool)
I think yo have something going on in your MachinePC that is causing MACH3 to stall or hang up from time to time.
Easy enought to test post a copy of the Cut file and we can test the Gcode.
Just a thought, (;-) TP