Miltoniopsis brow leaf tips.
 

miltoniopsis leaf tips turning brown. Much worse on white varieties

Welcome to the Orchid Board!

What are your growing conditions? Miltoniopsis prefer evenly cool temperatures, bright light, high humidity, good air circulation, low mineral content in the water and never to dry out.

70-60 day night, 50% min humidity very soft water. LED lights. Green house can get into the eighties in summer. No drying out.

When you say very soft water, you mean naturally, not from a water softener, right? Artificially softened water is loaded with sodium, which could do this.

Leaves dying back from the tip usually means insufficient water uptake for the temperature / humidity or too high mineral load in the water. My guesses would be insufficient humidity, excessive heat or not enough water. Did it happen recently, or this summer?

This plant might have different genetics from the others and be more sensitive to issues.