Install wireshark on your laptop and have a look at the packet capture.
Do you see any errors?
Check the logs on both sides, do you see anything out of the ordinary there?
I've personally used Movi/Jabber Video over a VzW 4G connection with no issues.
Could you check the IP Address which you get from your 4G-ISP on your device?
I assume you connect to the VCS-E, anyhow on such questions please describe the used environment.
The VCS-E might get "confused" if you get a public ip address which is firewalled, as
the VCS expects you can send and receive media without blocking.
Either use a VPN tunnel giving you a private ip / nat or ask your ISP if you could get a
private ip with NAT.
In some rare cases ipv6 could also be the impacting factor.
If it is the FW detection issue:
You could escalate this to (your) Cisco (Partner) to file a feature request for better FW handling
like fully implement STUN with a secondary IP, options to force traversal for specific clients
(like setting on the vcs, provisioning prameter via tms, ...)
Please remember to rate helpful responses and identify