for me all links are ok so it could be the first start you had. restart TTS and try again. another reason could be some regional blocking of some URLs... can you access all of them with a browser?

Restarting TTS doesn't help and I can access all the URLs with a browser. At least I was able to figure out a workaround.

The collider file seems to be the only problem. I downloaded the collider file and saved it locally. Now I can change the collider file to my local version when the Import Custom Model dialog appears. It's a little annoying because I have to do it several times, but at least it works.

I wanted to change the collider URL in my savegame file, but there is no result when I search for the URL.