Hi, I am wondering how do you use two range extenders in the same network?
Like MR3420 ))) (((TL-WA730RE ))) ((( TL-WA850RE, that's to say, WA730RE repeats MR3420's wifi, then WA850 repeats the wifi from the WA730RE?
It's not recommended to use multiple repeaters as the above, since this will slow down the wireless connection speed.

If you can connect to internet fine while the signal strength shows 0%, i assume it might be a display error.
How do you assure the two range extenders are working?
As to the extended range, the position of the range extender matters. Range extender should be placed in the middle of the router's wifi range; otherwise, it won't pick up good and consistent signal from the router, let alone to amplify the the signal.

Did you find a resolution to the 0% signal? I have the same equipment and problem.

Thanks
Doug

What's the firmware version?
Model number of your modem?
You can access internet but 0% signal, right?

I am also facing the same kind of problem.

Firmware Version: 3.15.9 Build 140912 Rel.35984n
Hardware Version: MR3420 v2 00000000

Device Using: ZTE 2766

Router Working Fine, Just Its Showing Signal Strength: 0%

[ATTACH=CONFIG]1902[/ATTACH]

Click refresh button and check if 100% appears.