That's really odd; I don't have a V3910 myself but I'm assured that syslog works. What I would do (and I appreciate it's tedious...) is back the V3910 and then start with a very simple default config and just syslog running - confirm it works, then adding settings in, work out at what point it stops.

I had Draytek Support look at it yesterday. They think the Firmware or config is corrupt, even though the FW is functioning fine (Mostly). They tried to use the packet trace to troubleshoot function and it just didn't work, the START button just flickered. We did the same on another 3910 and the START button did work for the packet trace.

They've asked me to do a factory reset. Sadly, the office is 3 hours away and access now is difficult. This will have to wait a few weeks till I can get access.

I've got syslog working with the latest beta for the 3910 and it worked fine with 3.9.2.2. The router isn't doing anything fancy though.