masdevallia leaf drop, without signs of rot

[pseymer]

I'm sort of new to growing masdevallia, but I'm trying to find information on why a masd. (Bella Donna) would drop leaves with no visible signs of stem rot. All of the leaves are a healthy green color, but periodically two to three leaves fall....the only thing I can think of that might cause this is heat spiking during the day...

The confusing this is, where the stem of the leave separates from the rest of the plant....it looks like what I would think stems would look like if a tiny animal had chewed on them (wish I had a photo) to separate them. There is no discoloration, and the leaves do not appear to be wilting or under and other sign of stress.

I'm hoping someone else has had this problem, or knows what could be going on. thanks in advance.