I have a kubota l3901 serial number 63355, after a parked regeneration the check engine light beeps every second and there is a total loss of power.
The symptoms you describe lean towards an existing problem within your aftertreatment system or emissions system on your tractor. When regeneration shuts down as a result of an existing fault, you will get these symptoms. Unfortunately, the only way to know which circuit or circuits have detected a problem is to retrieve the fault code information. Without that fault code information, one would only be guessing at the infinite possibilities that could exist within your after-treatment or engine emissions system.
When regulatory faults are ignored and the tractor continues to run, the ECM will default to derating to force the operator to diagnose and repair the problem. Once a derating has occurred, repairs would need to be made and the appropriate dealer level diagnostic software would need to be connected to reset all components in the aftertreatment system software to eliminate derating for the normal functioning. This sometimes requires a reprogramming or reflash of the software with the most current updates in order to reset the system after repairs are made.