This. The minable.result isn't being set properly when the entity is cloned.
If you want to fix it in the mean time, go to %APPDATA%\Factorio\mods, find ev-mining-drills_3.1.0.zip, and extract the ev-mining-drills_3.1.0 folder inside it to that same \mods directory. Now open mods\ev-mining-drills_3.1.0\space-age\drills.lua in your favorite text editor. Go to line 122, and insert the following line immediately before the data:extend line:
big_drill_mk2_entity.minable.result = big_drill_mk2_entity.name
The whole block (lines 114-123) should now look like:
big_drill_mk2_entity.name = "big-mining-drill-mk2"
big_drill_mk2_entity.icon = mod_name.."/graphics/icons/big-mining-drill-mk2.png"
big_drill_mk2_entity.max_health = 500
big_drill_mk2_entity.heating_energy = "300kW"
big_drill_mk2_entity.resource_drain_rate_percent = settings.startup["ev-mk2-drill-resource-drain"].value
big_drill_mk2_entity.mining_speed = settings.startup["ev-mk2-drill-mining-speed"].value
big_drill_mk2_entity.energy_usage = settings.startup["ev-mk2-drill-energy-usage"].value.."MW"
big_drill_mk2_entity.module_slots = settings.startup["ev-mk2-drill-module-slots"].value
big_drill_mk2_entity.minable.result = big_drill_mk2_entity.name
data:extend({big_drill_mk2_entity})
Save file, reload Factorio, problem solved.
