When I add 3rd powerline adapter, LEDs indicate slow speed connection
I purchased a set of two TL-PA4010(US) nano powerline adapters (in a kit). Because I wanted to have three powerline adapters, I also purchased a powerline range extender kit because it was on sale, and I was told that the one TL-PA4010(CA) adapter that came in that second kit could be used with the previously purchased TL-PA4010(US) to form a network of 3 adapters. (I am not using the range extender that came in the second kit.)
However, what I find is that any two of the adapters work well together - either a (US) and a (CA) or a (US) and a (US) - however, when I bring the third adapter onto the network, the speed LEDs on at least one of the adapters intermittently flashes orange and sometimes red (indicating a slow speed connection between the adapters). I also notice that I loose internet connection to at least one of the PCs attached to one of the powerline adapters.
I installed the TP-Link PLC Utility on my PC, and monitored the adapter network. This utility (also) tells me that speeds between any of the adapters (the "powerline rate") regardless of how I configure them is consistently below 50mbps (even if I have only two adapters on the network).
The one TL-PA4010(CA) adapter is a Ver 1.0 adapter, and I found that there was firmware available for it on the TP-Link website so I downloaded it and updated the adapter. This made no improvement.
I'm wondering what might be the issue.
F.Y.I. I have set up my powerline network in an apartment building, but the building and its electrical system are only 10 years old, and my apartment has its own separate electrical panel (though it is not metered separately). I have experimented using different outlets around the apartment with the same results. I also have all adapters plugged directly into electrical recepticals. One more strange thing: the orange and red LEDs usually flash on just one of the adapters, and I find that after re-setting the adapters (unplugging and re-plugging, and not always in the same order) I find that it is not always the same adapter that flashes orange or green.
Thanks for any help you can provide.