Sounds to me like a fuel problem,my push mower did this and what happening to mine was the primer valve would get sucked in and was getting to much air and kinda sputter then die in about 10-15 minutes.
Im sure your rider has no primer valve but still could sucking in air someplace,you know it has nothing to do with spark or plugs because it starts up,which means you are getting spark.
Or maybe you have a short someplace.