I run a wireless ISP. If your 900 wireless is intermittent, get the ISP to fix it. I haven’t generally found much that can’t be overcome eventually with effort and a little trial and error.
Raising the antenna, re aiming, etc, are often the real fixes for 900 intermittency.
for the most part, 900 can fool the installer, by having a stronger “bounce” than direct signal, and the installer will point the antenna at the bounce, which turns out to be dependent on weather, temperature, etc.
If nothing else, it’s also possible to do inexpensive “relay” sites. I can build a 900 relay site for about 700 bucks with the equipment I use, and it works very well.
I’ve talked with them about a relay. There’s a house down the road that seems to have better luck. They are friends of ours and the provider would consider such an option if all else fails. They are only about 100 yards away, if that.