Powerline adapters not playing nice with RT-N66U

I used to have three Aztech Powerline HomePlug AV adapters that I swapped out for three TP-Link Powerline adapters as I wanted to upgrade them to the faster AV2 standard. I heard that AV2 and AV were compatible with each other, so since I wanted an additional homeplug, I used one of the old Aztechs as my 4th homeplug.

However, I noticed that my router kept crashing after installing the 4th Homeplug. Thinking that it was the homeplug's fault, I replaced it with another TP-Link, but the...

Powerline adapters not playing nice with RT-N66U