yep. metal roofs cause the RF to bounce around.
Have had same issues…also having same issues in trailer park…
you definitely have to get them to the edge or get them elevated.
The reason metal roofs can cause so much trouble is that they act like a mirror to the RF signal. This results in the SM seeing the direct signal, and reflected copies of the original signal that arrive slightly later, because of the longer path via the reflective surface. The same signal arriving out of sync with itself will, to varying degrees, cancel itself out. Think of a sine wave. If the reflected signal travels farther enough than the direct signal, the reflection can arrive 180 degrees out of sync and effectively cancel out the intended direct signal entirely. What you see with the reflective surfaces is a varying degree of phase shift and cancellation.
Bodies of water, even a small pond or a swimming pool can kill it also… Unless it’s raining, then the surface is sufficiently disturbed, thereby reducing the reflective qualities. Resulting in "Why is my download speed faster when it’s storming outside?"
If it’s not glaringly obvious, we learned this one the hard way.
I try to always not shoot over any part of a roof because even a shingle roof covered in water can have this effect. A 3-4’ elevation plus narrowing the beamwidth by using dishes or yagis can help a lot.
I’ve had issues with 900 when heat waves are coming off non-metallic roofs as well.