WordPress or my host?

Wondered if I could run this by you. I had an issue yesterday where my site was just timing out instead of loading, just getting nothing at all. Then it would come back for a few minutes then go again. It was eventually down for about 9 hours until 1am. I need to find out if this is likely to be a configuration problem or my host.

Neither frontend nor admin would load. I had made no changes to config nor theme. To troubleshoot I disabled cache (during a moment the site was loading), no change. I repeated with my security plugin, again no change. I uploaded a clean htaccess file and enabled debugging in wp-config. No change. I renamed the plugins folder to disable them all, no change. I deleted the functions.php file in my child theme, no change.

At this point I had run out of ways to troubleshoot wordpress. The error and debug logs had nothing relevant (just some php notices). So I was thinking it must be the server. I tried changing the php version (the site had been running for months without a problem), no change. So I added a phpinfo file to my root so I could see if that would get a response. It just timed out. The server stats show no problems with resource usage at any time. It’s a shared server.

My host admitted they had made an error in the DNS records (missing NS records in the Active DNS zone) and fixed this yesterday. The site has been working so far today.

So my question is, would you say the likely cause of this is a server/dns issue or is there something else I can look at to troubleshoot?