@Jasmyn Did you try to reset them all and pair only two of them for a test? How to Reset the Powerline Adapter to Factory Default | TP-Link United Kingdom Also check if there is any IP conflict...

@Conrad-A Red led means the weak signal between the power adapters as UG here. Clear the home appliance near the socket and check if there is any new device in the house, try unplugging that first....

@Rickkins The speed degrees in the powerline according to article here.

@GeRmAnM They still do not have a driver for Mac OS Monterey yet, not sure if this is gonna help, I found someone posted this work for mac OS12 How to let my USB adapter works on the Mac OS big sur

@MH10 I would suggest reinstalling the driver and try some steps mentioned in the Step4 Cannot connect to Wi-Fi.

@SageDepiazz If would install the latest driver for the adapter and here is link. Download for Archer T2E | TP-Link I found here guide that offers some suggestion for slow speed with the adapter....