I have the 4G board also but my motors are not the same as yours.
By the sound of your motor, it sounds like your gearbox either needs grease or the ramps may need to be changed?
I recently pulled off my X motor gearboxes and inside it looked like there was hardly any grease on the gears. I put grease in and after reassembly they sound like you would expect them to sound - nice and smooth.

This has not eliminated my X motion problems though because just tonight it happened again.

I've been dealing with X motor problems ever since I got the 4G upgrade - intermittent ones that happen for no apparent or obvious reason. The motion sounds as if it's slowing when it shouldn't, or sometimes I'll hear a sound like it's jammed against something but it's not, and then it has missed steps and either tweaks partially off the rails or it's just not located in X where it thinks it is.

Things I have changed:
Disconnected and reconnected all wiring at the WAGO connections, even cutting off ends and restripping all wires.
Changed out my Geko X motor drivers with the Y and Z drivers
Changed the location of the USB plug
Used a (Shopbot supplied) powered USB hub
Stopped using the supplied powered USB hub
Changed computer settings so that the absolute minimal Windows services and programs run or don't run
Have no internet connection, no network connection, no updates, no virus program running
Make sure my control box is not on when my air compressor cycles on - even though it's a different circuit, it causes missed steps
Changed pinion gears, made sure the set screws were insane tight
Changed the turnbuckle tension in 1 turn increments anywhere from loose to too tight

I don't know what else to do. After it screwed up again this evening I was wondering if some of the ramp settings should be changed. I think if a ramp setting makes a movement too abrupt or aggressive, theoretically it could cause missed steps but, like you, the problem only happens in the X movement direction. If it was a ramp issue, I would expect it to happen in any direction.

Maybe the 4G board itself has some kind of intermittent short or part that's failing?

Another thing that bothers me about this control board is it creates such radio interference that I can't have my FM radio on with the control box on. My original control board never did that.