at least no problem on 10.10 with an iMac, FM13 Webdirect hosted at FMPHost and all latest updates for the Mac.
I know that you are pretty experienced with Filemaker etc. etc.
But could you share som info on the setup, network etc.
I assume that Webdirect is working with the localhost connection and from other computers on the LAN.
- Can you still access the servers standard web-server or any other services from the wan?
- Are you sure the internal/software Mac OS 10.9 firewall is not changed?
- How about network router/firewall and nat - are they pointing at the correct IP and open on all relevant ports?