Husaberg FE650 2006 stopped and backwheel locked

Hello guys, i have been riding my husaberg 650 for about 20hours. total of 426hours on speedometer. the other day the engine kind of died off while i was driving in about 60km/h. when i pulled in the clutch the engine stopped completely and when i let go the backwheel was locked (didn't turn) in about 60km/h. afterwards the compression felt kind of weak/low but when it cooled down it got better and i was able to start it. couldn't feel any loss of power but runs a bit poorly in idle. when i got home i did an oil and filter change (motorex 10W-50) and adjusted the valves. afterwards it ran nicely a couple of trips, but when i was driving today i only got about 2kilometers/5minutes away from home and then it happened again. I am suspecting it might be one of the piston rings has been damaged by heat or something like that. both times it happened i had plenty of oil and cooling water. but sometimes it's leaking a little bit of cooling water out of the hole in the side of the water pump cover. guess i should change the impeller seal? also curious if someone here maybe know what could cause this? very grateful for answers!

Couldn't see any swarf on the magnet when i did the oil change. also the filter was clean. i don't think it's the ignition because it seems like the problem just comes when the engine gets hot. and atleast the spark plug looked like it was in good conditon when i did the valve clearance. but i might change it just to test. do you think it could be anything else? really can't afford a piston change right now.. but a question about the backwheel locking, is this normal because of the high compression or is this a sign for problems with the piston/cylinder?

Is this an okey color of the spark plug?
exactly what am i looking for if i remove the left cover? do you know a good site to buy engine gaskets? really limited with parts for these bikes in norway..