I have a 1999 Komatsu WA320-3MC that shifts into gear goes for 30 ft then goes neutral. Same fwd and Rev also when it shifts. Select lever back to neutral and it will go back in gear and start over
Not sure what dash it was, but I used to have a 320 in the fleet that often had the same problem. It was usually a worn out relay.
Are the relays behind the dash?
On that machine they were under a cover behind the seat