First the terminology: I presume you're referring to the structure that forms at the top of the pseudobulb from which flowers emanate. That is the "sheath".
"Blind" sheaths are very common in immature plants, and sometimes occur in plants that are undernourished or had insufficient light levels to buid up their strength.
I will only briefly address the fact that there is no such thing as a "bloom booster" fertilizer, but nutrition should be given adequately and regularly throughout the plant's growth cycle. Waiting for the formation of a sheath to do so is too late.
One other thing I thought of - if you have been feeding it regularly, but with a high-nitrogen fertilizer, that can suppress blooming, as well. Goring to the lower-N formula can reverse that, but again, it needs to be done well before blooming is anticipated.
Ray Barkalow, Orchid Iconoclast
Treat Your Plants Right
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