After fiddling with why two motors were problematic I decided to remap them to different ports. This required the use of Cleanflight’s CLI, and the details provided by Joshua Bardwell in the following video was invaluable:
Now to reassemble the toaster in full and run a test flight. I expect this to be quite top heavy so we’ll see how long this build lasts.
Specifically, I remapped motor pins 3 and 4 to 7 and 8, respectively.