@dhenski 

Hi, based on the screenshots, the M7350 has received 4G signal but internet status is disconnected, please make sure the same SIM card works fine when using with other 4G device, then please follow the instruction below for troubleshooting:
https://www.tp-link.com/support/faq/794/

  @dhenski 

Hi, please confirm internet never works on M7350 or it works but loses internet access sometimes?

Please go to Advanced->Dial-up->Dial-up Settings page, check if the current APN profile is correct or not, if not, please create profile manually and enter APN etc. manually to check internet access again.

In addition, may I know the hardware and firmware version of your M7350? and if you have any other different SIM card, please also have a try in M7350 to see if internet works.