This is a strange one, and at the time of writing unresolved.
I have been working on a WordPress site quite happily and not noticing any unusual slowness. When someone else checked the site their response was that it took forever to load, my reply was that loading times seemed OK, but the next day I found out what they meant.
It appears that the first load of the day stalls and typically takes around 30 seconds, the first 25 of which appear to show absolutely no activity, just a blank white screen.
I performed a series of tests and here’s what I found:
The slow load (around 30 secs) seems to happen only for the first device to do the first load of the day i.e one morning I first loaded the site on my iPad which took around 30 seconds, then it was fine on my laptop and on my phone on 4G. So I believe the issue would only affect the first person to load the site each day. I have tried different variations, all of which support this.
I disabled all the plugins and the theme and the hang was still present but loading was not as slow (around 15 seconds).
I copied the site to a different host and never had the issue. It’s not super fast to load but never 30 seconds.
So my theory is, it’s a hosting issue which affects the first person/device to load the site each day, almost like the server is caching the site before it responds.
I will take the issue up with the hosting company and post the results here.
Update: 28th November
After much testing and several calls to the hosting company I didn’t make much progress. Eventually the hosting company said that as far as they were concerned everything was running fine. So I moved the site to another host and the problem disappeared (and the site was a lot faster in general).