IPv6 & mDNS Implementation on Cisco WLC2504 / Netgear Switches -- 2

I have configured a WLC2504 myself that works and is in use but needs to be configured by an expert, especially in regard to mdns / multicast.

The task will be to check the existing configuration in relation to the environment (residential), recommend/change settings to achieve best performance and reconfigure multicast / mdns so Spotify Connect and AirPlay / Screenshare work properly. As for now when I restart the mdns devices, they appear properly (Spotify connect / AirPlay), but disappear after a while. Also my device names (MacBook / iPhone) keep adding incremented numbers to their names (e.g MacBook (2747)), this should also stop. The network is very sluggish / slow when trying to connect to it and sometimes it takes multiple tries.

Furthermore I’d like to activate IPv6 on the whole system, so the modem, switch and wlc, etc. need to be configured.

The setup is as follows:

There is a central netgear switch Netgear GS748Tv5 (http://192.168.178.23/), no management functions active, that has the following devices connected (wired):

internet modem / router Fritzbox 6850 LTE (http://192.168.178.1/ -> WiFi banana_backup)
-> When I connect directly to this, Spotify / AirPlay works fine and all devices behave normal

Cisco WLC2504 (http://192.168.178.23/)
-> works for a while then Spotify_connect devices disappear

Audio server
-> hosting the Spotify_connect / AirPlay devices

Netgear GS110TP POE Switch (http://192.168.178.54/)
-> connected to the central netgear switch, powering the Cisco wireless access points

Please only apply if you have experience on the above devices, especially the WLC2504.