The most common cause of short flower spikes tends to be to much light.
Have had this a few times with some paphs ,i now leave the higher light for the Roth's & Roth hybrids.
You did not mention fertilizing regime but looking at the the rest of the information you have given
i expect you have that sorted.
Temps in your grow room should be fine , very similar to mine & i have had 1 or 2 huge spikes in there