So after replacing the faulty TL-SG1005D with a TL-SG1008D, the issue has been resolved.

@Kevin_Z After some more testing I seem to have narrowed down the issue to my switch (which I failed to mention). The router has 3 cables, Deco B, my desktop and a 5 port TP-Link switch. The switch...

I recently purchased 2 Deco M9 Plus units after reading many positive reviews about them. After installing both units I switched them to AP mode and connected all my devices. Both units are connected...