It is indeed related to the issue you linked. That one was however about installing LMS, which we can fix, while we cannot control how LMS internally accesses its plugin repository.
LMS has been renamed to “Lyrion Music Server”, and the URL has changed as well. The repository is now available at: Enhanced Digital Output
LMS v8.5.3 however still seems to use the old domain downloads.lms-community.org, even that it does not work anymore without following redirects. And these redirects are very slow when trying for the first time. On repeated access, it works better here, so probably it works well for you when trying it multiple times.
I discovered the problem was with the dns provider I was using (Cloudflare family - maybe it doesn’t like the redirect). Moving to the regular 1.1.1.1 solved the issue
This surely was not the issue, but as I said: Trying it multiple times already speeds up the redirects for me, hence I am sure the “solution” was that you retried it, not the changed DNS. Sometimes certain routes other other parts of the connection are cached, hence work better on subsequent attempts for a while. It can hence happen that you face the same issue again tomorrow, resp. when you want to install/upgrade another plugin. Simply retry it multiple times then. I hope LMS is changing the internal URLs soon.