Look around the forums here and at DSL Reports and you'll see plenty of people experiencing issues like yours with the Quantum hardware. Unfortunately there are a bunch of threads about the problems.
Check your splitter. Make sure it's moca 2.0. If not you'll need to get one.
@SinCara wrote: Check your splitter. Make sure it's moca 2.0. If not you'll need to get one.
That is not necessarily true, considering many of us that have the problems have MoCA 2.0 splitters.