I'm seeing something consistent but odd lately. For the past several weeks, accessing various stack exchange sites from home, sometimes a simple refresh of the page causes very slow load times. While pages normally load in a matter of seconds, when this occurs, it takes up to several minutes for a page to load, and if it doesn't time out altogether, it will load without CSS or images.
The problem is not with my internet connection as I can access other internet sites without issue, and even stream audio or video. In fact, it's not even a problem across all of Stack Exchange. What I'm seeing is that usually one or two stack exchange sites load slowly, but others are unaffected. For example, I regularly have tabs open with Stack Overflow, Code Review, Computer Graphics, Game Developers, Photography, and Movies & TV. Of those, only 2 or 3 will have this problem, and the rest will be fine. After about 10 minutes, the problem goes away and they all load as expected.
I see in some related questions that it has been suggested to try on other connections such as mobile phone. I haven't tried that yet (will do the next time it happens), but given that it only happens with a few sites at a time, I don't know what that would tell us. I will try it when I get a chance, though.
I'm curious if others have seen this, and if there's any sort of issue that needs to be looked into? It seems like it could be a CDN issue, or it could be something at my provider or someone upstream, though those last 2 seem less likely given that some of the stack exchange sites load fine. If it matters, I'm usually connected via Frontier from Southern California.
Update I happened to hit the problem with Code Review just now (5:10PM Pacific time, Sunday, April 16). I tried it on my mobile phone and it loaded instantly there. It failed to load on my laptop at all. Reloading a minute later, and it works just fine on the laptop.
Update 2 It occurs to me that hen I loaded it on my phone, I was still going through the same provider. I had wifi on, so it was still loading through my home internet connection, not through my mobile connection. Perhaps the mobile site doesn't have the same problem?
Update 3 I just solved a major piece of the puzzle, though I'm still confused. The problem appears to be with Safari on macOS. I recently moved and have a new internet provider, but the problem persists. So when I saw it happen, I opened up Firefox and went to the exact same page that Safari was having trouble loading, and sure enough it loaded fine! So same connection, same machine, same time, but different browsers. Clearly something's going wrong with Safari, but I don't know what. If anyone has any suggestions on how to debug further so I can send Apple a bug report, I'd appreciate it.