Lightroom Classic 12.3 Download issue (403)

Hello,
I am experiencing an issue while downloading Lightroom Classic 12.3 via our internal Update server. As soon as I click on "Install" the error 403 appears.

We set up the internal server about 2 years ago and it worked perfectly fine. Since the latest updates were downloaded via AUSST this issue appears. I even tried to download the updates again but nothing changed.

We are able to install all CC Products and even Lightroom Classic 11.5 but if we try to update or freshly install Lightroom Classic 12.3 the error appears without starting the download. The solution from https://helpx.adobe.com/creative-cloud/kb/troubleshoot-download-install-logs.html#error403 won't change anything. I logged out from Adobe CC and even uninstalled the whole application -> same issue. It also appears on different computers.