Leaf drop in seemingly healthy plants can be caused by many things, including shock from change (be it light, temperature, different food, change in water schedule), brushing up against the plant, a cat playing with it, mealybugs, root rot, needing to pot up, cold drafts, insects, fungi, etc.

Pics help a lot!

My advice:

Check plant for mites, insects, fungus
If any of the above are present, treat accordingly

Check the roots
Are they firm, white/cream/green? Or are they black or mushy?
If mushy/black, take cuttings of the plant and start over-root rot!
Is the plant rootbound in its pot?
If yes, is it overly rootbound (roots hanging out of bottom of pot or not able to be covered by potting medium).
If overly rootbound, pot up to a pot no bigger than 2 inches larger than the pot it is currently in (if you are using a 4 inch pot, don't go bigger than a 6 inch).

Check the potting medium
Is it well draining and "fluffy"? Or is it soggy, compacted and poorly draining?
If it is not draining well and is soggy/compacted, time to change the potting medium. Many on here will suggest using 1 part fine orchid bark, 1 part turface (or perlite), and 1 part crushed granite. All parts should be relatively the same size, meaning if you are using 1/8 inch orchid bark, you should also use 1/8 inch turface (perlite) and 1/8 inch crushed granite. If you cannot find some of these ingredients, from experience, my lacunosa did just fine in fine orchid mix (the bag contains perlite). Make sure your orchid mix does not contain peat moss.

Are you over or under-watering? Lacunosas like to be lightly damp. They should not fully dry out between waterings, but also should not be overly moist.

Check for critters (pets and children or other adult humans). Is the plant accidentally getting brushed against or knocked around (I have cats-they are sneaky).

Hope this helps!

Thank you!