if you use the 4G connection, suggest to check the WAN IP on the MR200 is a public IP address or not.If it is not a public IP address, better contact with ISP , request for a public IP address

As far as I know, there will have compatibility issue between different routers and USB stickers, even the same model.but due to the hardware or firmware difference, it may not compatible Suggest to...

when you go to the quick setup, during the process, need to fill in some info, such as PPP username , password, choose connection type , all the info need to provided by ISP.

when connected to the LAN port, able to ping the QNAP NAS on the PC? any guest network on your router? Maybe you can contact tp-link support team on support@tp-link.com, they will response

When in access point mode, modem to the 801ND is cable connection; when in repeater mode, 801ND wireless to the modem have you try to change a different cable? Other devices works fine when in access...

When you chose other type, the same blank? Have you reboot the router before go to he log? When restart the router , it will clear all the logs