I've never heard about any Toyota engine spitting out a plug. I know Ford had issues with the V10 spitting plugs. Sounds like at the 194 plug change the mechanic didn't tighten it enough and as it loosened up it messed up the threads. When you installed the new plug the damage was done but seemed to seat fine but caused a ticking time bomb. I'd Heli-coil that thread and go from there. It's pretty easy to do and doesn't take much time plus it saves a ton of money. Good luck.
New England Tundra Club Member #16