My router Linksys wrt16nl is running OpenWRT 19.07.2 r10947-65030d81f3 is using USB LTE modem Hyuawei E3372. The configuration is up and running without canges for almost a year without any issues.
Today out of sudden the connection to the Internet got broken. Checking the LTE interface in Luci it said "Network device is not present". I have unplugged the device from the router and connected it to Windows 10 PC and connected to the Internet using the provided driver - it connected succesfuly - modem should be OK.
If I change the device to /dev/ttyUSB1, the error is gone a virtual interface LTE_4 appears (as when it worked) and there are even some TX packets in LTE Interface. But no luck with the internet.
You have the old good E3372h in the right configuration and with the proper firmware.
Just configure it according to the instructions you mentioned - remove dialnumber, use device '/dev/cdc-wdm0'