Please Help - What Is It on my Grammatophyllum leaves?

[TOMMYMIAMI]

Ok, so with growing collection and purchasing 80 plants in last 2 months I guess this was just about to happen any time. I have never had pretty much any issues prior to this summer. So please, help me, what is it on my Grammatophyllum leaves. They were fine the whole summer but this week I am starting to see some issues, and I do not see any SOB on the plant, so not sure what beast is causing this and HOW TO STOP IT. It somehow started to appear after I did remove the protective sun cloth that I had on thee front of the plant during the strong summer sun, I removed it some 2 weeks ago since I think the plant is already used to the full afternoon sun but this does not look like sunburn to me???