The only thing I can think of is that you might want to check the status window to see its rank pips. The background is hard to see and you can't use a mixed faction Doff. If that isn't the problem, do you have other maintenance doffs equipped? Is it the battery or Engineering team Doff?
Foundry: Yet Another Borg Mission
It's terrible but easy, and these Borg are way cooler than the mess STO and Voyager left us.
May not actually be "way" cooler or even "slightly" cooler.