UPDATE: While trying various things/connection options etc it seems it is temporarily working (BT connected consistently and with music playable from Dudu, calls tested and working fine). I can reboot Dudu head unit and I think I had brief initial connection issues again, but after forgetting connection on only phone and rebooting, waiting for Dudu connection request prompt and then pairing via phone prompt it connected fine (after very quickly deselecting Media Audio to connect option on phone, under DUDUAUTO BT settings).
A number of days ago, I did manage to get a consistent connection several times, but as soon as I reboot my phone the same issues mentioned in OP above happen again. So I am very reluctant to try a phone reboot to see if all works OK-ish.
For further info, please see attached log which was captured after successful BT connection established and music playing... Before I rebooted Dudu to get log.
Many thanks for your attention on this