Phaleonopsis with small translucent / sunken spots on leaf

[greentiger87]

I've noticed the sudden appearance of translucent/sunken spots on on leaf of a noid phal. It was munched on by a caterpillar last year, but has recovered nicely - may have the healthiest roots of any of my phals. Gets morning sun, and full shade the rest of the day. With other phals that show no problems. Doesn't match any obvious issues, so I thought I'd ask here.

Wiping with a tissue shows no evidence of mites. Spots are small, no more than a few millimeters. Visible from both sides of the leaf, but obviously sunken on the underside.

Thanks in advance for any advice!

Pictures hopefully attached...