I have 2 AP's 903 running 1.4.3 currently and a 2865AC router running 4.3.1.1 without any major issues, with the exemption that from time to time the AP I mainly use disconnects from the router and I can't ping the router at all without restarting the AP and wait for it to reconnect and all is fine again.

I know there is a fix in firmware 4.3.2 around the mesh disconnect problem. So I upgraded the router to latest firmware 4.3.2.1 and when it restarts the AP's can't connect to the router at all.
The router states that the mesh network is all connected, but from the a connected device on the AP (wired or wireless) they can't connect to the router, ping also times out.

I have to downgrade the router back to 4.3.1.1 to get the mesh all communicating again.

Note: both AP's are wireless connected to router.

Has anyone been able to get the Mesh working on this configuration.

This may have been resolved in the 4.4.0 firmware which has just been released.

See https://forum.draytek.co.uk/viewtopic.php?t=24613 for a similar MESH issue

Currently this is only available only the international DrayTek site, the UK BT approved version hasn't been released yet

Latest AP903 firmware is now 1.4.4