GX440 and Static IP on VZW

I am running second time into the same strange problem with GX440s on VZW.
Verizon issues a set of consecutive public static IP addresses for my project.
With all GX440s online and communicating perfectly well with external networks
some of them cannot communicate to each other (no response to mutual ping commands).
I can’t find a pattern but it looks like close IP address numbers have something to do with it.
Both Verizon and Sierra tech support teams are trying to
convince me that there is no problem on their side.

The problem is real and I am dealing with it currently on two separate projects
(two pools of consecutive Static IPs). One of the projects was working well with
Raven XTs on the same IPs and the problem started when GX440 replaced old RXTs

Any suggestions?


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