Well, C. usitana is still a bit of a mystery to me...I failed at this plant twice when I started growing orchids and went on to other species in the Coelogyne genus.
So I'm afraid I can't give you any specific recommendations for this plant...
However, amongst my orchids I've had several doing the same thing as your C. usitana. Do great, go to sleep for a while and then...nothing!
As far as I'm concerned, I just kept treating them as if they were in winter rest and waited it out. Although I work with natural lighting, which might get the plant to start off new growths more readily than when working with artificial lighting.
Anyway, sticking to your questions now...I don't thinking forcing the plant to grow/bloom/do anything at all using fertilizer is a good idea, you might end up damaging the roots as they are not active at the moment and thus further destabilize the plant.
Temperature might be the issue, but I'm not that certain. I know plenty of professional growers in Belgium who grow theirs in intermediate conditions and they've been doing great!
My gut tells me you should give it a light boost (maybe combined with some temperature rise?) in order to politely tell it it's time to get moving.
I basically just wrote down everything that went through my mind...I hope it was of any help!