Incoming Calls being mis-directed to second line - or not ringing at all

[Whenenrome]

So we have a new Ooma Telo, with 4 HD3 handsets, and two lines - the main number, and the second number - two handsets exclusive to each one. It's been great, and at certain times, all over the place.

Outbound calls place successfully, always. They do occasionally have issues with other caller saying that we're cutting out. Never hear that complaint on an incoming call.

But the real, major problem, is actually receiving an incoming call. One of two things can happen:

1) An incoming call is made to the main number, which rings momentarily, then before it can be answered, stops ringing the main number and starts ringing our second number, who picks up the call successfully. The caller realizes they've reached the wrong number.

2) An incoming call is made to the second number, but nothing rings on the handsets. The caller hears 5 rings before it goes to voicemail.

Everything is set correctly, in terms of one pair of the four handsets being assigned only to one number, and the other pair to the other number exclusively. Is my Telo super confused? Possibly defective? Is the DECT 6 setup just not stable enough to pull off the 4 phones split between two lines?

We love the potential of Ooma, and what it can do. But when it's not working correctly, which is happening too often in a matter of a few weeks, it can be frustrating. Any feedback is very appreciated!