I am stable 12h+ blend, IBT but I got random reboots just browsing www or watching movies.
Sounds familiar, i'd like to hear if you find solution for that.
On my own system, just like yours IBT/LINX/PRIME/HCI MEMTEST stable still random hang ups sometimes. Few notch vCore have always solved this issue but i cant see any mind why Idle state needs more vCore than fully loaded system?