even vanilla and not i often dont have more than 4 drones in any depot until almost space with the exception of many key depots or long distance related ones.
I can remember your save, the 'stack size' mod, changes it from 10 to 500 drones (basically the progressbar was fine for 50 drones max, way less for 2500) makes me think I should enforce our own mod setting stack size, after all other mods (since it's already a setting)