If you ride hard and bang something around repeatedly, things wiggle, wires flex, existing corrosion flakes off. Anything is possible in a wet environment. Mine ran fine for 2-3 weeks after cleaning up the fuel system, and started cutting out and dying on me. I thought it was the carbs again but the plug on top of the black box by the battery looked as normal as every other plug in there. After taking it apart I found very rotten wires at the soldered wire connections within the plug. My key stopped working and I found very corroded ground wires inside that same box.
I'm saying these are some causes I've seen for what you have described. The heat seizing is a long shot and hopefully not the case but looking at the plugs is easy and could provide some peace of mind. You could also feel the engine and big pipe when it happens for additional peace of mind. They should be hot but not so hot you get burned. You should be able to stand touching it though. If your beeper works when placing the key on, it should warn you of overheating that way. Test the post first following the article on here somewhere. It too goes bad pretty unexpectedly if no other symptoms occur when this is happening.
