If you check https://tools.wmflabs.org/iabot/index.php?page=manageurlsingle&url=http%3A%2F%2Fwww1.wdr.de%2Fmediathek%2Fvideo%2Fsendungen%2Faktuelle_stunde%2Fvideotebartzvanelstraeumtvorwuerfeein100.html, you will see the the bot whitelisted the entire domain. This is likely because the bot has detected that the bot is being blocked from accessing the domain, and thus cannot determine if it is dead or not. You will have to tag the link manually and let the bot run over it.

Ok thanks. So, for my understanding*: After manually tagging a URL as dead and running the bot again on that article will the bot then recognize that URL as dead in future when scanning other articles?

*I think about mentioning such cases (and what to do) in the local FAQ

Unfortunately, no. It used to do that, but that created way too many problems on enwiki.

It will treat the URL dead only on pages that tag it dead. I can of course un-whitelist it to see if IABot has access to it again.

The last scan was on 16:41 2 December 2017

I don't think that's worth your time in this case. It's more about me understand the general process. Thanks!

Un-whitelisting only take a few seconds to do.

okay :-)

And done. Give it a try now.

Worked fine- thanks!