Kohler Generator issue

Finally after three months of lockdown have been able to get down to the boat. Replaced the salt water pump (previous thread) and brought home the battery which was flat to recharge manually. Somehow the breaker on the switch panel had been turned off and charger wasn't running even though I was running generator...lesson learnt.
However after running for around 25 minutes the generator shutdown as if the Stop button had been pressed. Quick check of the fuel and didn't feel all that hot it started right up again and ran fine anither 10 minutes or so before I shut down manually as was running out of time.
Kind of stumped as to how to troubleshoot that one?
Also notice that the voltmeter on the switch panel on the helm was at first flickering and the just showed zero volts. I suspect a Vlad fuse I popper to check may not have gone back in properly, but can anyone think of another reason for that behaviour

Apologies for long post!

Simon, the panel for the genset will have a switch to select either shorepower or genset,as the power source. Easy to forget to switch over.
Running a genset a long time with no load can glaze the cylinder bores, excess blue smoke is an indicator, 25 mins should not be long enough, and it should still run, give it a good hour test run, with load, like the water heater, an electric heater,fridge compressor, etc. The Onan book says you should run weekly for 1/2 hour.
If we ever get locked down again,Maritime`s site it was ok to visit the boat for checks and maintenance, and it wasn`t LGA limited. I kept a print of the page in the car in case we got questioned.

BruceK - yep was checking that panel when I noticed the breaker was in the OFf position.
Going back Friday and will try it with the load, pretty much just the fridge normally. I looked all over the health dept sites but didnt think of looking at the Maritime site!