Miltoniopsis flower spike rotting and breaking
 

I bought my first miltoniopsis plant. It arrived with the beginnings of flower spikes. They grew beautifully over the past month or so. The plant looked very happy growing in my bathroom in indirect sun and good ventilation. However, on my daily check, yesterday, I was upset to see the beautiful spikes had suddenly started rotting and breaking. All I could think was a sudden cold snap - from about 25 to 15 degrees Celsius- might be responsible, or that maybe even the stake was too short. I honestly don’t know. Could anyone help me? The plant is Breathless Brilliant, and I don’t overwater it. Here is a pic.

Your temps are both at the low end (day and night) for it, but not horribly low. Are you watering it enough? As you say you're not overwatering... They don't like to dry out. How does the potting medium look? They don't like decomposed potting mix.

Is it in large bark? If so it could be watered daily.

The medium has never dried out. Actually, one flower spike - a more immature one - is still in good shape. I check the medium every day.

Follow up pic of miltoniopsis rotting flower spikes
 

I’ve circled the less mature spike that hasn’t gone the way of the others.

The plant looks dull green and water-stressed to me. When these are happy they are vibrant bright light green and lush. They are best in cool, airy, very humid climates, where humans would need a jacket. I haven't been to Australia - have you been to a cool, dripping moss forest? Or a cloud forest? Or a forest in the fog? That is the climate Miltoniopsis like.

I thought the leaves would get pleated if the plant didn’t have enough water. I’ll just water the plant every day from now on, and let it fully drain before putting it back in its spot. Thanks to everyone for their suggestions.

The pleating only forms on leaves as they're expanding. Already mature leaves don't do that.