This is a dedicated topic for the Flint 2 'low data mode' detection issue that came up on a forum with a different topic. I've created this topic so that anyone else with the same issue can follow up.
The setup
Plug in a 4g dongle in the usb port (Huawei E8372-608)
Connect and set the dongle as priority 1 in the multiwan tab
Set a failover WAN on Ethernet 1
Load exhaustible data bundle on the 4g dongle
Connect/tether the dongle under Internet tab
Result
Once the dongle exhausts carrier-allocated data the Flint 2 will not detect loss of internet and failover to Ethernet 1. It will continue staying connected to the dongle despite lack of internet access.
Note
I can access the default carrier website but not any other website. I believe this is what the ‘low data mode setting’ is for but it doesn’t work as intended yet. This issue is recurrent on 4.5.8 stable and 4.6.0 beta.
Acknowledgment by devs
The issue outlined above was confirmed by one of the devs and we're hoping for a fix soon.
It should switch over to the backup interface right? That's the thing...it doesn't. I have also tried using a dlink lte router and connected to the second 2.5gig ethernet port on the flint 2. Still it will not fail over to a backup lan when data is depleted in the sim of the dlink router.
The original problem was that Flint 2 was not failing over to backup LAN when the depletion of data in main internet source (tether set as 1st priority) did not induce failover to the backup LAN. It was suggest I try 'low data mode' to see if it will fix the issue but it didn't. My Flint 2 will not failover irregardless of the low data setting. @_zhang acknowledged a problem with the code and would work on a fix soon.
I have started testing 4.7 beta. I will focus on the multiwan low data option and give feedback here. Thanks so much for the changes. I will try the 3 options low, normal and strict.