Look into the temperature profile they are receiving. Orchids are CAM plants (they photosynthesize differently from other plants) night time temperatures are very critical for carbon fixation, if they are too high or too low then the plant will not photosynthesize, use up its stored carbon for respiration and eventually die. Neofinetias get the most amount of light during the winter and spring in their native habitats, may be even if they are in rest that could be a key to good growth? Anyone with experience in Neos, can you corroborate this?
Check out this link about culture suggestions
Culture of Neofinetia falcata -