Sometimes the ARD Mediathek works but mostly not at ONE TV

Maybe I'm totally at the wrong place wrong and I don't know the right category - Sorry, I'm a new user of Zyxel.....

So, I'm using the ATP200 on an 100/40MBit (Yes, it's lame .-( ) PPOE-WAN to my ISP. After the box configuration the most things gone well! But some things are - let's say - not clear:

So, the most worried think is the use of the ARD-Medieathek (Germany). At first, nothing worked at any Samsung TV (using the SmartHub). No YouTube, no Amazon, no Mediethek. After some troubleshooting I found out, that if SSL3 or less is dropped, mostly streaming services doesn't work. (Drop connection in case of HTTPS connection with SSL V3 or previous version at "Web Content Filter").
After that it got even crazier: I deactivated this blocking and on every TV every (used) Service worked well, except for one TV (Samsung UE70RU7099UXZG). For this one YouTube and Amazon are working but not the ARD-Medieathek. Sometime streams of these Mediathek are shown, but mostly not. Have you some Ideas??

The other thing is my (and others) android phone. Sometimes, but more than once per day, it lost the internet connection. I think it's more a measurement problem. How does google or android detect the internet connection? Maybe a simple ping to a Google server? I don't know, but I think it does it regularly and sometimes it doesn't work (is blocked by the ATP200). Her again: Have you some Ideas??

Thanks a lot
Oliver