Every time it rains or gets windy, I lose the same 20 or so HD channels. This has gone on for years. They still work on the non-HD side but they are either totally pixilated or simply not usable on the HD side. I have had techs at my house four different times and they have updated/switched out almost everything inside the house but it doesnt help. One tech said its where my FIOS wire connects to the main service at the pole but she didnt make any attempt to fix it. My neighbor suggested having Verizon change out the white box on the outside on the house where the wire connect but I dont know how to get Verizon to do this. Any thoughts - its really annoying and I've been paying full price for non-full service.
Lots of possibilities. MOST Likely its your "inhouse" wiring. Particularly check out your connectors at the ONT, Your splitters, any Barrels (often at wallplates).
The 20 channels, may be in the higher frequencies, which are often effected by wiring problems.
It sounds like a splice in the fiber is bad or has a dirty light. If there was a fiber cut anytime in your hood, this could be a culprit. Ask repair to check.