2021 Yamaha yz250f starting issues/intermittent

My bike died at the track after 6 laps/ cut out. Got back to the van, started up no problem then run on the stand for couple minutes then cut out. This went on a number of times until eventually the battery died.
I’ve put on a new battery and the bike fired up straight away then after 30 seconds died again. The bike runs perfect until it cuts out. Now the bike it’s clicking the starter relay but will not crank. You can hear the fuel pump buzz and the click as you press the button.
I’ve took out the starter out and tried directly against a battery and no problems with the starter.
Any ideas I’m starting to get lost now. Maybe main relay?? But can’t understand why the odd time the bike will start and run perfect then just cut out then will start and cut out a few times then just cuts out and won’t restart
Thanks

The bike has 43
Hours from new and well maintained