KTM 125 SX 2017 Seized randomly before going out for next practice session

It was a good day until it wasn't 🤣

I was riding Saturday finished one of my sessions of about 20 minutes. Back to pit area & turned off bike normally. Went to go out for my next session about 30/40 minutes later & the bike was seized solid. Couldn't get the kick starter past halfway & in gear you could pick the bike up from the back wheel it was solid. My piston was checked through the exhaust port 2 weeks ago & I've put about 4 hours on since & at the time I was told the piston looked good but I know this doesn't rule of the rings. Nothing has been opened up to have a look but I'm curious if something like this has happened to anyone else. The bike was running fine no issues, no bad sounds or anything.

I'm sceptical about the air to fuel ratio as the person who does the main work on the bike changed the main jet as the mentioned the bike was over fuelling causing excess fuel out of the exhaust. He couldn't remember whether it was a bigger or smaller jet he put in. Since the jet change there was less excess from the exhaust and the bike seemed to run better I'm just curious as to whether this could've played a part.

I'm all new to this with the maintenance side of bikes but I'm trying to learn as I go as only been riding bikes 8 months after about 16 years when I had a bike as a kid & dad took care of it all 🤣

Any help/advice would be appreciated. Thanks ✌