Set the client to be WDS, but you set yourself your AP as you’d normally do, without WDS. Then you go in Luci and search the WWAN interface and check that it’s blocked like a WAN port, also make sure you don’t use the DNS of the router you’re guest in. You can do not that much wrong, just try. And yes obviously, WDS is for that purpose. I had never a problem to just remove the guest interface or anything I couldn’t explain myself, I would even suggest you try to do let have the clients also just regular client mode instead of WDS. Worked for me every time so far, plus, try if you can connect after you changed the mac address of your A750.
With the router my ISP set me up I do that with the AR750, it was no problem to set the 2,4ghz + the 5ghz one time as client in wds mode and the ohter two in access point mode without WDS.
If that’s for any reason isn’t working take a look at Dynapoint or similar opkgs, try setting up a shadowsocks for yourself etc. but it doesn’t seem to be worth the effort and the GL-UI is buggy when it comes to this, use LuCi to check your stats, so no worries, you get it working for sure.
wlan0 * SSID: GL-AR750 - Client (WDS) (I wouldn’t hide the SSIDs at all or not too soon, hidden SSIDs and WDS are no friends) setting up the connection, sometimes obviously that’s device specific.) or your mac addy gets blocked because of two many “failed” attempts**
*** wlan0-1: GL-AR7502g– AP (AP) (Which is buggy, you have to do that in Luci) **
*** wlan-1: GL-AR750-5g – AP
*** wlan-1-1: GL-AR750-5g - – Client - WDS (ONLY)**
**that does the trick.**
Also is is it not an option to let the WDS be WDS, use OLSR mesh or Dynapoint or inaydn, alred or batman? I think the first two are far easier to use and are a luci-app. Or better: Nothing you just don’t use WDS / Mesh. .since I never felt a real improvement in stability or anything, anyways. Besides that it is slightly faster when both are complete without encryption but hidden.