VDSL modem keeps disconnecting

I've had FiOS for the last three years. Unfortunately my complex doesn't have actual FiOS to each unit just to the building and uses VDSL to connect to each unit. Everything worked fine for a while but then the VDSL modem just started disconnecting and reconnecting over and over again. This will go on for hours with at least 20 disconnects an hour. Twice so far I have had Verizon techs come out and both times they have replaced the VDSL modem. It will usually work for months no problem now it's doing it once again. Just wanted to see if this was a wide spread problem and their hardware is just this bad or if there is something else going on maybe in our building setup. Any thoughts or help would be appreciated. I really don't want to have to deal with support again and get a tech out her but it looks like that's just what I have to do to have decent service