Q: How do I use our WWAN and LAN connection at the same time in Windows 10?

A: Windows 10 has a group policy called "Minimize the number of simultaneous connections to the internet or a windows domain". This needs to be disabled. This group policy is located here

Group Policy>>Computer Configuration>>Administrative Templates>>Network>>Windows Connection Manager>>Minimize the number of simultaneous connections to the internet or a windows domain>>Set to disabled and apply