Why does my temperature suddenly drop to zero?

Happened twice during this roast… everything else seemed normal - but you can see how the IBTS curve dropped to zero and then rebounded a couple times:

regular link:

It is the bean probe that drops to zero (not IBTS). You might have a damaged probe or a bad connection to the control PCB. Did you recently clean the front plate?

Yes, I cleaned it about 10 roasts ago! Is this something I can fix myself?

You can check the connection from the bean probe.
If you took apart the inside stainless steel plate and put it back together you might have routed the bean probe wires incorrectly so that they are squeezed between the black alu front, and the stainless inside plate. This creates a short especially when the bullet heats up.
You can also check the crimps in the white connector housing that connects to the control board.

Cool I will check that. Is there some schematic or picture showing how the wires are supposed to go when you close it up again?

There is a slot in the black alu front they have to stay inside.

So I opened the front up again. I realized I had misunderstood, I have not previously opened the alu plate - just the black front plate to the drum. So there are no cables that could have moved.

I cleaned the bean sensor metal part and closed again, and the next roast was OK. I hope it stays that way!