Perhaps double side tape under the device and one side tape above the device. Actually you may consider to replace it with a EAP device. This can be mounted on the ceiling.

Make sure the NC450 is with the latest firmware and your phone is with the latest version. The 24hr recording needs to work with a sd card. Is the SD card recognized by the app? Do you see a blue...

Does your device support 802.11K&V? 802.11K&V can help device to achieve seamless roaming. If your device doesn't support 802.11K&V, the device may disconnect from the wifi when the signal is very...

There may be some other special default settings on the switch . You may troubleshoot like this. Connect a PC to the second deco via a cable and check what's the IP address the PC get. Hope you can...

Is the first deco configured as router mode?

Did you try the latest firmware ? http://www.tp-link.com/en/download/Deco-M5.html#Firmware If your deco untis are still not stable, you should feedback to tp-link support.