What Might be Causing this Bud Blast/Flower Drop?

[vlhart]

Hello!

This Brother Sara Gold phal appears to be in some kind of distress. The flower you see has only been open for two days. As you can see in the backlit photo, the leaves of this phal are extremely thin, almost see-through. It had somewhat thin leaves when I bought it 2 years ago. In the spring/summer of 2015 it had a big growth spurt and grew 4 thin leaves and lots of roots very quickly (but no flowers). I did notice that during that summer, it seemed to be oozing sap from the leaves quite a lot but there was no sign of pests then.

This summer it grew one new leaf but all the leaves seemed to be getting thinner and duller (losing the sheen). I had a big thrips problem last summer in a different room in the apartment and found some in this plant, then in the fall I saw a few black/grey tiny mites in this plant and some others nearby but I no longer see that many. I treated it mostly by wiping the leaves clean, or submerging the leaves in water (carefully to avoid water in the crown) and trying to knock pests off.

It lost two leaves last week (one pictured here) before the first bud opened and another appears to be going leathery. Any thoughts on what might be happening? I'd like to save the other two buds if possible.

It's in a SE facing window that does get into the 60s at night, high 70s-low 80s during the day. It's possible that it had some cold damage as the leaves were touching the window at one point? The roots seem to be in great shape.

Thanks for any advice!

[url=https://flic.kr/p/RH5nvL]