Epithechea with black blisters on leaves

[Nitsuj]

I have had this orchid for many years but last year it started developing these black blisters on the undersurface of the leaves. The leaves started falling off more quickly than usual. And at first, it was mostly the older leaves that developed these black blisters. The plant is growing fast enough and producing new canes and leaves that I am not immediately worried about losing it. I do not believe it is sunburn because it starts on the lower surface first and the plant has been in the same location for years.
Can someone please help me identify the problem and any corrective actions?
Thanks

[estación seca]

Have a look at the diseases Web page of the St Augustine Orchid Society. It looks to me like a fungus.

[Nitsuj]

Thank you. Looks like a great resource