What could be causing this spotty extrusion?
I´ve seen this in my Prusa due two parameters that may vary your results depending on climate if your printer has not a temperature chamber or having a mechanical issue too.

Lack of extrusion is due a cold filament which it can't reach the melting temperature due a fast extrusion feed; I mean in normal conditions we can print @70&nbsp;mm/s with 195&nbsp;°C but on wet or colder days is not possible so I need to slow down the speed (feed rate) with 10&nbsp;% less than normal to get @60&nbsp;mm/s or less until get a good flow with out modifying the G-code. If I try to print faster on normal conditions I will get the same lack of material due 195&nbsp;°C is a low temperature (this is an example).

If I set the temperature 200&nbsp;°C or 210&nbsp;°C I will get a better flow and also print faster than @80&nbsp;mm/s (not affected too much on climate on 100&nbsp;% feed rate).

For first layer I´m using an speed of 40&nbsp;mm/s to allow a good adhesion and Z height 90&nbsp;% of layer height (0.22 typically or 0.18).

Mechanical side: The extruder is not feeding all the filament due a missing pression on the traction gear (filament slip).