XPS 13 2-1 (9365) and Dell PN556W Pen: top buttons stop working on reboot

I have a new XPS 13 2 in 1 (9365).

Also bought the PN556W.

At first it seemed everything was fine. Paired perfectly, writes well, top buttons open OneNote and can be configured in the pen control panel for other shortcuts etc.

However, every reboot/restart I need to repair the pen as the top buttons stop working.

- I notice that after a reboot the pen is reported as "PAIRED", but not "CONNECTED" in the Windows 10 bluetooth settings page.

- when I re-pair the pen, the status changes from "PAIRED" to "CONNECTED" again and all is fine until the next restart.

- sometimes when exiting sleep or standby the same problem will happen.

Any ideas ? Could this be a bug in Windows 10 Creators Update (1703).

Very annoying behaviour.