First some basic details:
*I have 2 offices one located in Kansas City and the other in Oklahoma City.
*Each office is equipped with an M370 firewall, the offices are connected via BOVPN connection and all server access is working as expected
*Each firewall has an active Mobile VPN with SSL configuration in place
*Servers are running WS2016 and all users are running Windows 10
*Users have network shares mapped via GPO in AD
Now on to the problem:
I recently followed the instructions on the Watchguard website here and confirmed that the settings were working properly. However, over the weekend I was informed by a VPN user in Kansas City they could not access server resources in Oklahoma City. The user confirmed that on Thursday evening they were able to access all mapped shares successfully. When I connect to the VPN and try to access a network share requiring the BOVPN tunnel I am told the resource is unavailable. When I attempt to ping the server I am unsuccessful. Manually attempting to access the server and its shares are just as unsuccessful. I have made no changes to the firewall. Attempts to monitor traffic via the firewall itself are not showing anything of relevance that I can find. Any hints or pointers you can suggest to maybe resolve this issue? Thank you in advance for any help you can provide.
How are you setup to allow hopping between local subnets via the initial ssl-vpn tunnel?
My users were unable to move between local subnets when connected over the SSL-vpn tunnel. (One of many issues why the company I worked for fired its MSP and brought me on full time). I put the tunnel routes in rules in place in order to allow subnet access while connected via the VPN tunnel. Which was tested and pushed into production on February 8, 2019. I’ve spent about 2 hours today with WatchGuard on the phone and have it confirmed that my settings are correct. The tech I worked with was unable to find any reason to discern why traffic is suddenly failing. They have since escalated the ticket and I am waiting on a followup phone call for further troubleshooting.
I haven’t updated the firewall firmware since I put them into production on December 1 and December 11 of 2018 respectively. I’ve thought about said reboots however I hate to take down the whole network at each site, even temporarily. However I will do what I have to if needed. I am still waiting on followup from WatchGuard escalation team for further support.
I’m interested and will follow - which version of the OS are you running?
does the sudden loss of traffic coincide with an OS upgrade?
I’m trying to implement this now - and not having much luck.
Difference in my setup - I have an SDWAN upstream from the watchguards - so I am not using BOVPN between sites.
I know the boxes are running XTM Pro, however I cannot find any specific version numbers beyond that.
My users are all on Windows 10, however they have various builds and versions. I am also in the midst of configuring a WSUS server to manage Windows updates and bring that piece under control. Another of the many issues related to the poor performance of the MSP 
WatchGuard tier 2 is currently analyzing traffic. I will perform a wide scale restart of the firewalls tomorrow evening if I don’t have a resolution or update from WatchGuard.
Are you managing in wsm, the web, or dimension?
Status should tell you os version.
When was last update applied? Both ends same version?