Wifi clients won't connect to TimeCapsule

I just had an odd experience I would like to share regards clients not able to connect to a TC Wifi access point.

Helping my neighbour with a more or less sudden wifi outage I struggled quite some to understand what happened.

Clients where not able to connect to the wifi - all got "bad password" , tried to update password - reboot the TC - all the same - not able to join.

If I disconnected the wan connection (the internet connection ) of the TC - Clients would connect just fine, but as internet was disconnected it wasn't mutch use.

As the TC was set in bridgemode the clients got internal adresses but once I connected the ISP it provided new IP adresses and connection to Internet was ok.

So why wouldn't it let new clients in to the wifi when connected to internet ?

Was suspecting the ISP to do some strange things but could not understand what it could be.

It then came to my attention that that a TV set top box was connected to the TC and - woala - disconnecting that let me register new wifi clients as mutch as I like while connected to Internet.

The thing where that the TV set top box where draining the TC for CPU/Memory to the extent it could not authenticate WIFI clients.

The TV stream with multicast and unicast streams where just to much for it to handle - using a port on the ISP modem instead of the TC solved it.

To be mentioned - the ISP is delivering on fiber connection so the capacity and bandwith is high.

Only the Internet capacity is 500Gb/500Gb - and the TV stream is on top of that.