Hi ,
regarding this issue with port forwarding we need to do some packet capture,
On RV180 we have the option to capture the WAN and LAN interfaces.
When you have the issue, connect to the RV180 and run the Packet capture on LAN interface and try to access to the server connected to the local network of the router, and capture the WAN and LAN interface we can see the packet where is dropped.
Please you can also call the Cisco Technical Support and open a ticket regarding the issue, better when you have the issue they can investigate and made the capture traffic.
here is the small business contact : http://www.cisco.com/c/en/us/support/web/tsd-cisco-small-business-support-center-contacts.html
Thanks
Mehdi