(Neither of my routers are showing on the dropdown menu, go figure)

Hello!

So, I got myself an upgrade from my:

N750 Wireless Dual Band Gigabit RouterModel

No. TL-WDR4300

Firmware Version 3.14.3 Build 150518 Rel.70901n

Hardware Version: WDR4300 v1 00000000 to a
 

to a

AC1200 Wireless Dual Band Router

Model No. Archer C50

Firmware Version: 0.9.1 0.2 v0093.0 Build 180313 Rel.54477n(4555)

Hardware Version: Archer C50 v4 00000002

I set up the C50 to be the main router/wifi and moved the N750 to be a WDS bridge. I got a few issues while at it. 
First random lag spikes, I mean the ping between PC to the WDS sometimes is between 100ms to Timeouts, like out of nowhere for no reason, normally its quite stable at <1ms to 10ms.

Second, I can't ping between the routers. I get "Request timed out" from both ends. Also, I can't ping anything from the N750 (WDS) I tried the main router (192.168.0.1) I tried 8.8.8.8 I tried 8.8.4.4 no problem from the main router. It can ping itself without a problem.

The bridge does work, not as I expected it to work as the speed took a dive but the range went up. 

Also, the last question, as both routers have dual-band, should I WDS both 2.4 and 5? Or just 2.4 (due to the range) and if I only WDS 2.4 can I still use the 5ghz band on the WDS? 

Thank you very much for reading and for the help, if you find any grammatic error feel free to correct me as English is my third language.