Based on this pic showing the cutter next to the gantry I suspect @DnKFab is right that your cutter very well could be causing the interference. Are any of the plasma cables coiled up? That can create interference as well.
Having made good cuts is just a function of luck with that setup in my opinion. I assume that’s your usb cable to the left of the plasma and that you place your laptop to the left of your cutter when you’re operating the system. Your plasma lead looks coiled up hanging in the table where it can induce electromagnetic pulses into everything on that corner. Your plasma is right next to the machine control box and your laptop and ur usb. I would say you’re very lucky it has ever worked consistently at all. You need the torch lead not coiled up anywhere near table electronics or usb cable. You need usb cable all by itself headed to your laptop. With as much distance as possible from plasma torch , plasma work cable (ground).
@Jjfablab like @DnKFab stated just lucky it worked but electrical interference can be moody at times. Move it as far away as you cables will allow and definitely dont have the cables coiled. When they are coiled think of it as a coil in an electric motor it is going to create strong electromagnetic fields and electronics just dont like interference like that.
My thoughts are the usb cable is the most sensitive to rf noise. Next is laptop and control box. I dont recommend putting plasma under table just for risk of flooding it with table leak. The little box that handles voltage for thc I think is just as much a problem as the main leads coming out the front of the plasma. When you think about it it has the same drastic voltage changes pulsing through it as the main plasma leads. Order of most important I think is get lap top and usb away from cutting table, and all other leads. Don’t coil your ground or cutting lead coils anywhere on your table. I think your power lead on the wall is probably fine. I only have one small concern there and it’s a bit of a reach. If you have your electrical I. The wall directly behind it you could be inducing noise into your line inside the wall. That is a very long shot. Ultimately you probably will have coils but they need to be away from the laptop, the table and the usb cord. That usb cord needs to be completely by itself. They do make longer double choked usb cords you can get on Amazon. The double choke is imperative.