Scenarios (assuming standard usage without mod or extra equipment):
1. Auto band mode - 2G/3G/4G signal is weak or unstable, a fluctuation in signal strength will trigger a need for more power and if not enough power is supplied to the modem, it will go into a state where you can't reconnect. The only way to get it to connect back is to unplug/plug back the modem or toggle USB power off/on from ROOter firmware. Might need to repeat a few times until it's connected. Another way to tackle this is either use external antenna to make sure the signal is consistent or to use single band mode.
2. Single band mode - change to a band that you know it has consistently good signals, eg: 3G only at 900/2100MHz or 4G only at 1800/2600MHz. Can couple it with external antenna as well depending on the needs

- It helps in most cases especially when you're in a very good signal area, but when a fluctuate of signal below a certain threshold, the modem will go into a state that doesn't allow it to reconnect
- Usually this will automatically be resolved by the ROOter firmware if you've "Enabled with Modem Toggle" select in the "Connection Keep Alive" option under Modem > Connection page
- Since the modem is connected to a powered hub, the power toggle doesn't really happen. The only way is to unplug and plug back in the modem.

- Many suggest a minimum of 2A output (voltage depending on your router's requirement)
- Some routers like MR3420V2 have circuit board that filter the power output of the USB port to 900mA/1A, using higher output power adapter might not help
- Router like MR3020/WR703N (not sure about MR3040) should be the best option as it doesn't filter the power output and the modem toggle works as expected