Temperatures are a bit high, but that's common for Prime95. You're not reaching throttling temperatures, so I doubt temperature is a real concern. Despite no major findings with Memtest86+ and Prime95, it could be an issue with your memory, CPU, motherboard, or PSU. See if running with only one 8GB module at a time helps. If you crash, switch to your other 8GB.
What are your voltage readings in your BIOS? HWMonitor is good at reading temperatures, but HWMonitor and other hardware readings within Windows are not 100% reliable at reading the true voltages.