The most common reason for tasks going "inconclusive" and then later "invalid" is an extreme overclock'd CPU, or, more generally, heat. I know that's probably not the answer you wanted to hear :-) An error that occurs anywhere along the way in the LLR work (like 321) will foul the result, so the longer tasks are more susceptible to that.
You have some TRP-LLR tasks that are inconclusive too. There is no known problem with 321 in general. I think the general wisdom would be to reset any CPU or memory overclock back to "stock" in BIOS, and see how things go there, and if "good", then maybe nudge the clocks up gradually. Blast the case and fans out with compressed air to improve cooling. LLR is a CPU (&memory) torture test. I had a box with an AMD CPU a while back and I did notice it was less tolerant of being pushed hard compared to Intel SB (or IB).
Check in here when you get a chance and let us know how it goes.