On this mower to verify you have a seat switch problem, which likely since they run 12v though it to operate a relay; unplug the connector at the seat switch and install a jumper wire and then test. If the problem goes away replace the switch. For some reason when 12 volt positive is ran these normally open switches it tends to burn the internal contacts then you get intermittent problems.
Note> Remove the jumper wire after testing,
DO NOT survival race leave it in place as it disables part of your safety system.
Stens 430-413 and Rotary 9663 are replacement switches for the Kubota K1122-62280 switch.