Using viewer 7.1.2.0, host 7.1.2.0 and ru-server 3.2.1.0
ru-server is hosted in a DC, viewer and host are on different business-grade connections
My problem is as follows:
- Host shows as online
- Attempt to connect (any action, doesn't matter)
- Instantly get 'Unable to connect. Attempts left: ' dialog. Host now shows as offline
- When dialog times out after 5 attempts, host will show as online again after a short interval
Here is a short screen-cap demonstrating the issue:

A temporary solution appears to be to restart the ru-server, but this doesn't always last very long. The issue varies in how frequently it presents.
I suspect something happens with the firewall in front of the ru-server that the ru-server/hosts don't recover from or the lack of IPv6 on the ru-server (most of the hosts are dual-stack with IPv6 connectivity but the ru-server is not currently configured with an IPv6 address)
This is quite problematic for us as not all operators have access to restart the ru-server (not to mention it is very frustrating when it does it multiple times in longer support sessions).
Any help greatly received.