So then I assume you’re also using a valid registred domain name. If Nextloud is running on the same host as the desktop client, you could add the following to your hosts file…
127.0.0.1 cloud.yourdomain.tld
…and then use your actual domain name instead of localhost.
Btw, regardless of whether this is actually a bug, I’d recommend that everyone ranting in this thread take a look at 101: Split-Brain DNS (Split Horizon)
A proper split-brain DNS setup allows you to use the same domain name/URL inside and outside your local network, which has several advantages. For example, when creating and sharing links or if you have mobile devices that sometimes connect from inside your local network and sometimes from the internet.