LS300 periodically unresponsive

We have 7 LS300 devices provisioned onto Verizon in Richmond and Tidewater Virginia. 5 of the 7 are reliably functioning as a gateway to reach from the Internet to a sign controller located adjacent to the LS300. The other two locations are occasionally (once or twice a day) becoming unresponsive to access from the Internet, including failing to pass the needed data to the controller, declining to allow access to AceManager, and refusing to respond to a ICMP ping. After between 30 minutes and 2 hours, the LS300 will again become responsive.

We have recently shortened the WAN watchdog period to 10 minutes and activitated the keepalive ping, which seems to shorten the duration of the outages.

The occurrences seem to be correlated to jumps in signal strength (from -80 to -55 or from -70 to -90) and changes in the reported cellular channel.

Has this happened to others? Is there a configuration setting to avoid this instability? Since this has not been reported in a RavenXT nearby one of the LS300 sites, I suspect that this is a reliability weakness in the LS300 firmware.

I had the exact same problem with a pair of Ravens on Verizon (a little over two years ago) - never could find a solution. Eventually switched to ATT and never had the problem again.