Welcome to the forum, hopefully we can help you out
Bear in mind that readings from Speedfan don't always correspond with working/active sensors, so they can't always be trusted. Having said that, I'm suspecting that your VRMs are overheating - VRM = Voltage Regulator Module, they're basically what supplies power to the CPU. Some cheaper AMD boards, especially MSI, are known for issues with power hungry CPUs such as the FX8300, and your symptoms sound somewhat like they're overheating. That said, I don't think TMPIN1 is measuring your VRM temperatures directly as they usually don't have sensors and can usually take around 100-105C anyway, but it may well be nearby hence the correlation.
There are two fairly easy ways to test this theory. One - if you happen to have a spare fan, or even if you use a case fan, just connect it up and point it to the VRM area on your board (this is to the left of the CPU socket, they're the small black square things) and run the test again, see if it lasts any longer with some cooling directed at the VRMs. Two, you could underclock and undervolt your CPU a little to reduce its power consumption, this will reduce stress on the VRMs causing them to heat up less - again if it runs for longer this would potentially point to a VRM overheating. Alternatively if you can disable turbo mode in the BIOS, give that a try too.
The VRMs on your board are specced to 95W which is in theory the FX8300's TDP, however there is evidence out there that many "95W" VRMs aren't truly capable of this, and AMD's FX CPUs don't always seem to adhere to their published TDP either, both of which obviously cause issues.
I'll stress that this is just speculation at this point, but at least it gives you a few things to try, to hopefully narrow down the issue a little.