This could very likely be an RFI problem, with RF getting into the PTT circuit. I had a similar problem.
Try reducing the rf output to A very low value say 1 watt, and see if everything runs reliably as it should. Does it occur on all bands ? Had problems here on top band , and only after messing around fitting ferrite toroidal did wsjt-x work reliably.
So much depends on how much rf is floating around in your shack.