Oh, wow. This sort of happened in my life!

My grandmother's house is adjacent my parents' w/ 200 ft. between and line of sight. Back in 2013, when my grandmother moved into the then-new house, I setup a point-to-point wifi bridge between them to share my parents' Internet connection and give me easy remote support access to grandma.

Summer of 2023 visiting relatives complained the Internet service in grandma's house was slow and unreliable. There were repeated suggestions made by helpful relatives for purchasing a new WiFi router for her house, getting independent Internet service, etc.

Grandma was happy with it, and the relatives went home, so I put off looking at it. When I did finally look at it, months later (when I went over for Thanksgiving) everything seemed fine.

When the relatives came to visit in summer 2024 they complained again. I looked at it immediately and found massive packet loss on both ends.

The ornamental trees planted along the driveway between the houses were the culprit. With the leaves off (say, at Thanksgiving time) it was fine. When the relatives came to visit in the summer the trees were in full leaf and acting as very good attenuators.

The trees were newly planted when grandma moved in. I didn't even think about them getting bigger and fuller when I set up the link. They filled out in the 10 years intervening, though. (Chalk it up to me still being relatively young and not thinking about installations on 10+ year timescales when I put it up.)

Fortunately there's a room in her house with line of sight to my parents' house unobscured by trees. It meant putting the radio outside a bedroom window instead of the attic (where I'd originally stashed it), but it solved the problem and ended complaints from relatives.