Help diagnose engine seizure

[scrambler250]

I was on a dual sport/adventure ride a few weekends ago and seized my engine. I was about 20 miles in, all gravel/dirt roads, topped a hill, and the engine shut down. I hadn't gotten to full throttle over that 20 miles, and wasn't pushing the engine particularly hard when it died. I had mixed Stihl Ultra (synthetic) 50:1 the night before with 87 oct. I usually use Bel-Ray H1R, but have run the Stihl mix recently with no issues. The plug looked good, maybe a little rich. The piston/cylinder had a four corner seizure. The worst scaring was on the intake/clutch side, and exhaust/flywheel side. Those corners both had a piece of cylinder plating stuck to the piston. I've only put ~15 hours on this piston & cylinder since replating. Is this seizure from a flaw in the plating process or just a lack of lubrication? I quit racing enduros years ago, and was hoping to transition this bike into some dual sport use, but is this type of riding (relatively consistent speeds over longer distances) more than what I should expect to be able to reliably do? Also, any suggestions on where to get this cylinder replated?