I just got a reply from the nursery where I got mine from.
"No way to be sure, but the light may be an issue. Also, like vandas, they are heavy feeders, so if you aren't feeding it regularly (we feed once a week at this time of year) it could be that as well.
Some of the flowering is dependent on the weather, too. The plants respond to the environment -- light, temperature, water. Some of these conditions may be too subtle for us to mark the difference (from one season to another), but the plants react to them. They do best with some light midday shade, especially in hot weather.
Some of ours aren't putting out as many flowers as they sometimes do. It happens, probably nothing to lose sleep over if the plants are otherwise healthy."