I'm really not an expert for such problems, but the issue may be cause by a lot of factors, i.e. the usb-cable is to long, problems with the com-ports, defect printers mainboard a.s.o.
For the experts it is very helpful to know more informations, such as the printer has worked before and the issue is new, what new components are mounted or other things have changed ...
I recomment to test it with a android tablet / smartfone and a software like this: GCodePrintr lite to be downloaded from the Google play store. On this way the issue can be isolated.
I'm using exclusively cards for both printers. Problems are unknown.