What kind of instability? I have both Hoppers connected with no obvious issues, at least none I'm aware of. I Sling off one, I have Joeys connected, one Joey per Hopper. I don't use the DishOnline services aside from Slinging. Joeys do show all Red in the MoCA menu, but MoCA bars are green, no HIC just hardwired Ethernet.
Physically, not the problem. Signal looping with 2 connections causing instability is the problem unless Hoppers are separated with an isolator. One connection is the correct hook up - to one Hopper with bridging enabled or one HIC connected with a tap into a Joey or a Hopper coax.
I guess I could disconnect one and see what happens.