Was interested when seeing this subject. I have had the same issue with the last two pairs purchased in Thailand. Very strange sort of waviness appeared on the lenses. Not really visible unless you had the right light and angle. First noticeable due to the the lenses becoming less and less effective at providing correction. At first I thought maybe my eyesight was deteriorating.
Eventually, when overseas, I had my eyes checked and my vision actually showed a slight improvement. By this time, I had identified the strange condition of the surface of the lenses, so I was purchasing a replacement pair. I showed the lenses to the optician, tilting them under the right light until she saw something. She said she had never seen this before, but agreed that it appeared to be related to the coating.
Haven't had such an issue previously (many purchased in Thailand), and have not seen it in the most recent replacement purchased overseas (3 years on). I'll try a different shop in Thailand the next time I need a pair over there (although hey probably all get sent to the same lens provider anyway).