My Home Pod Mini keeps disconnecting from WiFi.  It also fails to connect following WiFi Router restart.

The Home Pod Mini was returned to Apple for checking, and was reset then the latest firmware applied.

From online searches, this looks to be not uncommonly reported.

I'm wondering whether there are any settings in WiFi that enable Draytek Router WiFi better to integrate with Home Pod Mini.  

I have both 2.4G and 5G WiFi enabled, and both use the same SSID.  All other WiFi connected devices have no problem at all.  Only the Home Pod Mini is problematic.