Got new firmware (mine's at v1.0_191212 for Archer C5v router) that support the updated dongle. Contact maxis customer support ask them to update your router firmware.
Aiyoh brader, the 4G dongle for backup la, leave plug in router when fiber connection go down will auto connect, not for your to bring to work (ala portable 4G/Wifi hotspot). If works last time, u lucky, maxis haven't clamp down yet.

Got new firmware for Archer C5v router (See above) that support the updated dongle. For your case, plug ur dongle in the maxis archer c5v router, connect the c5v to fiber and contact maxis customer support ask them to update your router firmware to latest. Also pray that they haven't clam down that loophole.
Dongles should work plug and play with the new updated firmware for Archer c5v router. I have no problems on mine

I faced the same problem too at the same time as you. When I logged into 192.168.0.1 (the ZTE MF833V admin page) I found that it wasn't connected. I had to inspect html source and manually enabled the "Connect" button, then it worked.

After that I went to the Settings page and changed WAN Connection Mode from Manual to Automatic. Now it survives a router restart and connects automatically.