Some Github projects don't show up

Gentlemen, I am a first-time user of Travis (or planning to become one) and I am starting with quite a strange problem:

I installed Travis to my Github account. In the repository configuration of Travis I selected All repositories. Now lots of my Github repositories show up. But hell, exactly that one repository I was planning to activate Travis for does NOT show up.

It is this repository:

Also when not using All repositories but instead using Only selected repositories then I can select it but when returning back to the repository list of Travis (to configure) then it does not show up.

I googled alot already and read that I should try the Sync-button which I did but it didn’t help. I also waited several hours but still no luck.
Also I read that private repositories don’t show up either but that repo of mine isn’t private as far as I know.

Any ideas? I’m a bit out of luck. Thanks alot.