Yeah, I get this. We need to find out why so we can get this fixed properly. So thanks for staying in tough with us about this issue. Can you make out specific entries in either excludeClients or excludeDomains causing this?
I still assume it may be the fritz.box entry will all of your clients get a fritz.box suffix. Please try them using anchors, like
^localhost$
^fritz.box$
^iobroker.fritz.box$
^SKY-IPTV-WZ.fritz.box$
^SKY-IPTV-GZ.fritz.box$
^DiskStation.fritz.box$
^pihole-6.fritz.box$
to ensure fritz.box really matches only fritz.box and not also xyz.fritz.box (which does contain fritz,box).