Page / browser caching problem

There are 2 sites, a live one (www) and test/dev site (dev).

You might need to look at both. For instance, there is a plugin that shows the current & forecast weather, bottom right of the home page.

On the live site Chrome is showing up-to-date weather info, and today’s date in the header. If I open a new tab then load the test/dev site, it shows yesterday’s date and yesterday’s weather.

NB. I have been in contact with the weather plugin author and we have verified that the plugin is getting the correct data from their system – their widget retrieves data from a transient, if (transient) data is “old/expired” – new data is retrieved from their system. We have verified that the data in the transient is correct and being updated every 15 minutes. So in the above situation, the plugin transient on the test/dev site has got today’s weather data – you can view the data using the Transients Manager plugin – but Chrome is serving up a cached page from yesterday, not a page with today’s date and weather.

Loading Firefox today, it is still showing me Wednesday’s page, as per this: https://imgur.com/a/0L8wng8

If I launch Firefox today and load the live site, it is still showing me the page from January 23. Obviously if I did a hard cache refresh I’d get today’s actual page but I’m keeping the old cached version until we get to the bottom of this.

Doing the same with Chrome, I get the true live home page for today.

What I don’t understand is why something is not telling Firefox that the home page has changed since January 23 and to re-load ‘afresh’.

There are over 20 browser.cache settings in about:config for Firefox, none of which says ‘age’. Which one is relevant?

But as I reported in the original post, the problem has been seen in Chrome as well.

What does using incognito mode show/prove?

This is not a plugin issue. The home page has numerous plugins and elements and my original post mentioned that the date in the header was not being updated – this is just a line of PHP code – and that a recently published news story, served up by Enfold’s Blog Posts element, was not being displayed, but that the posts from the previous day were still being shown, along with the outdated weather, i.e. the browser was loading a cached page from the day before and not the latest content.

As I wrote in the original support request, and in a follow-up,

On the live site Chrome is showing up-to-date weather info, and today’s date in the header. If I open a new tab then load the test/dev site, it shows yesterday’s date and yesterday’s weather.
…and…
If I launch Firefox today (January 30) and load the live site, it is still showing me the page from January 23.

Despite multiple re-starts of both PC and both browsers, that situation endured for over a week. Neither browser would refresh correctly on its own, as it should.

Over the weekend however, without doing a hard cache refresh, the latest content is being shown by both browsers on both live and test sites. I have not changed anything but something has finally caused ‘normal service’. But I guess we’ll never found out what, as no-one has been able to replicate it or offer any suggestions as to what might be the problem. I will continue to monitor and watch for any re-occurrence.