The C3150 is not a 3G/4G router, it can't work with the USB modem, and can't enable second WAN connection.

Have you tried change the channel and channel width on the modem? If not, you can have a try. https://www.tp-link.com/en/faq-474.html What's the firmware and hardware version of your modem? If your...

For the deco unit, when you open the deco app, and then go to the More->Wireless->Password, if you want to unsecured your wifi network, you can delete the password, and then click on save. Then you...

May I know have you enabled QoS function and high priority function on the Deco APP? If yes, on the QoS, please choose standard, and please disable the high priority function for all the clients, and...

On the tpCamera app, when you go to the live view page, you can try to adjust the position of the camera focus by your own. Here is the picture.

For your issue, you can refer to the link below to do some troubleshoot. https://www.tp-link.com/en/faq-1790.html