Sounds like soft siezing due to running lean and not enough lubricant.
The piston overheats because it needs the fuel in the air to cool it, then under high loads it slowly grabs the bore causing the engine to stop. Each time it stops it does more damage to the piston and bore until the rings will jam and it won't start due to lack of compression.
On an alloy piston with cast iron bore and good lubricant, an engine can survive a few soft siezes and be useable. If you did not increase the lubricant and run the cylinder in for 500km, then you may have damaged the piston and bore.
When you change a piston and cylinder on a two stroke, it is essential to retune the carby to cope with the extra air being sucked into the bigger cylinder. Two strokes run great running lean but the heat buildup and other stuff will cause the engine to fail.
There is a good chance you have already damaged the piston and bore beyond salvage. When I upsized my engine, I bought 3 pistons and bores in-case I had issues. I did not have problems at the start but after many thousands of kilometers, a crack in the aircleaner caused a soft sieze and I needed to replace the piston and bore.
Welcome to the world of hotting up two strokes.
2001 Yamaha Zuma, DR Evo 68 cylinder, Leo Vince TT derestricted, Delorto 17.5 (#98 jet), standard aircleaner, RMS fan, Race CDI, Standard oiler and premix @ 75:1 Shell SX2, Doppler SR3 variator, RMS clutch, RMS R rear shock absorber and Pirelli SL26 tyres.