Steve, I think we may be getting to the problem.

Some instructions from the Plusnet forum about static IP addresses:

https://community.plus.net/t5/Everything-else/Dynamic-Static-ip-address/td-p/1927051

The Draytek "Dynamic DNS" application

(Applications -> Dynamic DNS) SHOULD update your DDNS service but there are suggestions that this has been a bit unreliable with some recent firmware.

Personally, with Plusnet I would go for a static IP every time.

In terms of your external (public) IP address changing the Draytek will keep this updated if your supplier changes this.

I can't tell you how often Plusnet changes the IP address for customers without a static IP address for obvious reasons.

Think back to your TCP/IP course and lease times....

Also thing like my Hive heating control and some wifi cameras are inaccessible, that could also be related to the router not knowing its proper IP address I suppose.

Thanks, I will look into static IP, I manage another plusnet account with a different setup and I know the IP address can change anything between a few times a day to once a week, so it would tie in with what I am seeing.

Well that was a nice interaction with Plusnet - I now have a static IP address but have not yet rebooted the router to make it take effect.

BTW this is what I was talking about with the VLAN settings, this on the Plusnet help pages, if it doesn't open at the right bit click What Setting Should I Use For Fibre Broadband...
https://www.plus.net/help/broadband/broadband-connection-settings/

You want the instructions for "What settings should I use for a fibre router that's connected to a BT Openreach modem?" as that's what you have.

This matches the Draytek instructions.

Don't touch anything there anyway as it fundimentally works.