I've bought a TP-Link TL-WA850RE powerline adapter a couple years back and it worked flawlessly. That was, until I decided to install a new firmware version. The connection is now considerably jittery, with spikes at constant intervals, and its speed degrades over-time as well. Restarting seems to fix the latter, temporarily. Rolling back to a previous firmware version doesn't solve neither issue. A while back I even sent a support ticket and made a thread in the official forums to no avail. I've also scoured through multiple threads with similar issues but unfortunately lacking any worthwhile solutions.

As an example, this is the result of a ping test through Windows CMD:

I've had it report 1%~3% packet loss in the past, but can't seem to replicate it at the moment. Regardless, it's exceptionally aggravating. I have trouble voice-chatting and playing online games for the most part. (And, yes, I am aware that these devices are not meant for these types of activities, but, and as I previously mentioned, the device worked properly in its first run, even while playing multiplayer games and voice-chatting online.) However, I can browse the internet and stream content impeccably. Downloads, on the other hand, vary from time to time, but are, more often than not, slower than I would like them to be. (Although a restart of the device, as I've said, bumps up the speed again.)

Eventually, I wound up resetting my router, the device, and my computer to factory settings - to start fresh. It didn't help. I'm honestly at a loss here, and have no clue on what to do. I'm no network expert, so I wouldn't know where to look for potential bugs. I've fiddled around with so many settings that I have completely lost faith in ever finding a proper fix.