I am having some trouble with a Nextcloud server. I set up a digitalocean droplet to test contact syncing for work. I went with the setup that I use at home, which is Yunohost and Nextcloud. This was/is working fine to sync contacts with iOS using the built-in support for CardDav accounts in iOS.

I made a snapshot of the server and rebuilt it on a work account (also Digital ocean). I reconfigured it for a new domain name, and got a letsencrypt cert. I can login and manage the admin and user accounts.

I set up an iPad to use the new server, and it seemed to work fine. However, I subsequently tried a couple other iPhones, and it won't connect to the account.

It isn't a fail2ban thing, because on the same apple devices that I can't connect to the accounts on, I can go login to Nextcloud in their browser.

What is happening?

Edit: I seem to have fixed it by reinstalling the server from scratch. I wanted to eliminate any problems that may have been caused by restoring from a snapshot previously linked to another domain. Everything is working at least for now.