all youtube links deliver fals positives

What status messages does the plugin show for those links? Could you please post a couple of specific examples (link URL and status)?

See for example on page https://www.oekologische-plattform.de/?p=1827

details in broken link checker:
URL: https://www.youtube.com/watch?v=Ajgm03ZHO04&feature=results_main&playnext=1&list=PLD920FA37AB2D3928

Error message:
Video nicht gefunden (video not found)
Konzerne blockieren die Energiewende Konzerne blockieren die Energiewende

Link zuletzt geprüft: 1. Juli 2015
HTTP Code: 0
Reaktionszeit: 0.496 Sekunden
Endgültige URL: https://www.youtube.com/watch?v=Ajgm03ZHO04&feature=results_main&playnext=1&list=PLD920FA37AB2D3928
Weiterleitung Anzahl: 0
Instanz Anzahl: 1

Dieser Link schlug 3 mal fehl.
Dieser Links ist fehlerhaft seit 2 Tage.

Thanks

Hmm, I added that to a test site and the plugin correctly detected it as a working link. Maybe the video was temporarily private/restricted and has been restored now? Try clicking the “Recheck” option under the link URL.

Recheck didn’t help. I already rechecked a couple of times.

Sorry, I’m not sure what else could cause that. Since it’s flagged as broken on one site and works fine on another, it’s probably something server-specific. Maybe the video is region-restricted and your server happens to be in a location that doesn’t have access to that video?

You’re right, obviously the problem was in the my installation. But I didn’t find out the reason. I solved it by deinstalling all the plugin and reinstalled. All works fine.

Thank You