check the 3g/4g ip address when internet stops working. if there is no ip address, which means this router disconnect from isp side using that sim card. You can put that sim card to your phone to...

do you want to separate users? if no, you can try this, setup tl-wr840n in access point. after the configuration, connect that cable from 841Hp to the lan port of TL-WR840N. you just need to...

you can try this. http://www.tp-link.com.au/download/TD-W8968_V2.html#Firmware the latest one, i think.

this M7350 doesn't built in with vpn. so you need to download some kind of vpn apps and apply for vpn services online. But there is a lot of vpn fraud so be careful.

never heard of that issue with dsl-6740u. try another port on the router? i think when the router is not working, it is normal that TP-link adapter won't work.

try a beta firmware http://static.tp-link.com/TL-WPA8630P_v1_1_0_3_up(170222)-20170222(EU).zip