Have you upgrade camera firmware to 1.4.0 version?
I have similar issue with my camera.
Then I consult tplink and got a reply as below.
After downgrade the firmware,it seems working stably.

Dear Customer,

Thanks for your feedback!
We already attached high importance on it.

We need to confirm information below to check this issue.
1. Is your camera connected by Wi-Fi or Ethernet Cable?
2. What's the light color when you found camera disconnected?
3. Please log in camera's Web UI by IP address and check if liveview could display normally.
4.It might be a wireless compatibility issue with the main router.
Please kindly tell me the model number of your router so that we can do further analyses.

For temporary solution, please downgrade the firmware version to 1.3.4 and check if the problem will be resolved.
Please do the following steps to downgrade it:
1.Please download the middle firmware and upgrade it via web browser.
http://support.tp-link.com/f/d4a690790c/?dl=1

About How to upgrade firmware on NC series cameras, please click on the following link to get some help：
https://www.tp-link.com/en/faq-1972.html

2. Please download 1.3.4 firmware and upgrade it via web browser.
http://support.tp-link.com/f/25d8dbff69/?dl=1

Then reset camera and do the configuration again.
And then check if it will work properly.

Thanks for your cooperation in advance.

Hi,

Thanks for the reply, yes I have the latest firmware 1.4.0 as it just upgraded last week so I think it's since then I have had problems. This time when they disconnected turning off and back on actually sorted them and they are now connected. If it happens again I will downgrade them using that link you supplied. Thanks very much for your help.