Although 3.6.1 appeared to be better than 3.6.0, I still did incur one SIP registration drop and so have reverted to 3.3.7.1.

2 firmwares not good?Can ask each firmare are you using "all" or the "rst" file?
Draytek recommends the rst and configuration all from scratch for each new firmware and not use of other previews firmware back up files
But if you have too many settings, leave the firmware that works for your needing s with out extra hassle of time which may still not work
Thanks for your time

Confess I always use the .all file and hold over my configuration settings. I could consider using the .rst and then restoring a saved config backup, but re-entering everything from factory scratch by hand would be too high a price to pay.