where do you grow it? (im assuming outdoors) it could be that your humidity may have fluctuated or dropped low enough for
the spike to abort? or maybe something is chewing on the spike? I had that
happened to one of my vandas before, I noticed that the spike is about to emerge about
1cm when something got to it and chewed it up. Also if your growing outside in full sun, it could
be that some water stayed in between the leaves and when the sun got it, it may have
burned the emerging spike, happened to me too, but the spike continued to develop and bloom.
I doubt that stagnant water stored in between the leaves could have done it, I water my vandas
at least 2x daily, and often the last one is done late in the afternoon at aroung 5-6ish... but im
growing outdoors so there is constant air movement.
Of course dont take my word for it, im sure someone more experienced can give you better advice.