Interesting... I personally have had one hopper fire in my PG500, actually it was more of a smolder because I happened to catch it and stop it before it go too bad. Mine happened immediately after grilling steaks, I had been operating at like full speed or close to it, and then shut the grill down and walked away. Every since then, I've been more careful about that... I now, always reduce the temperature and let the grill stabilize at a lower temperature ( like 200F or so ) for a while before I shut it down. So far after I've started letting it gradually cool down with lower set temperature , I've not had any further issues with auger tube fire... I've owned the PG500 for almost two years now.
I've cooked at least 8 times , where I was running at over 600F for more than an hour preheating and cooking pizza... and never had hopper fires afterward. Now, after I did these high temperature cooks, I dropped the temperature down to 200F or so for 10 or 15 minutes before turning the grill off.
Anyway, I do know it's possible to have auger tube fires in a PG500, but for me... I think I've been able to avoid these by merely turning down the heat for a while before shutting down.