they should be all compatible with each other, so you may try different wall sockets, and try to exchange the v2 and v3's location to have a test(make sure the house light on v3 are on as well which means they are paired)

First of all, update the V3 ones to the same firmware level that your V2s have.

Peter M wrote

First of all, update the V3 ones to the same firmware level that your V2s have.

And how do you do that when the same firmware level isn't available? I have tried to use V2 firmware on V3 devices and vice versa and it fails. So what is your secret?

Could this V3 adapter just faulty? You may try only plug V3 pair(only two adapters, no V2 any more), then check if there is any speed issue.

Enson Loo wrote

Could this V3 adapter just faulty? You may try only plug V3 pair(only two adapters, no V2 any more), then check if there is any speed issue.

Maybe, but I got a replacement new from Amazon and the exact same behavior from the replacements. The device works, I think the problem is in the application. The lack of firmware and application updates seems to be a pattern across many chinese vendors as Reolink and Linksys Velop devices suffer from slow support.