after k2 upgrade to 2.10.3 pages and k2 modules often not updating for days until clear browser cache (mostly chrome)
sometimes while it works properly it suddenly displays content from 3-4 days ago
random if hit refresh on browser button displays newest k2 articles but if after click on homepage link displays older content
Joomla 3.9.18 Gantry 4 php 7.3
module cache + page cache on

I am having the problem too, this is my first installation of K2 so very new to it.

I am using Cache Cleaner of Regularlabs since a long time and this normally solves the problem.

So here is the link to where I am playing with K2 at the moment but would like to implement the Joomla articles soon.

family-historian.com/t/latest

I think I am seeing a similar problem. My wife has a news site that she's been building with Joomla + K2 + Gantry 5. All the articles are K2 articles and some pages use K2 content modules. A few months ago, she noticed that often when she changes an article in the back end, it doesn't change for the client with F5, but does with ctlr+F5. If I am looking at a single K2 item, it does refresh correctly, but if I look at a page with a list of articles in a K2 content module, it doesn't refresh correctly. Actually the browser is requesting a page, but since the Last-Modified date is not changing, server is returning HTTP 304 and the browser uses locally cached version. Today I noticed that when this started to occur was around the same time K2 2.10.3 was released, and the patch notes do say something about changes around Last-Modified header. The current behavior is clearly not right, so I wonder if we needed to change some setting when updating to 2.10.3.

Using Joomla 3.9.19
Under global configuration, Cache Settings:
Cache Handler: "File"
Path to cache folder: blank
Cache Time: 1
Platform Specific Caching: No
System Cache is "OFF"
Page Cache plugin is disabled
I'm not aware of any other cache plugins
When I look at the "clear cache (site)" page, it shows one cache group, "gantry", with zero cache files.
Are there cache settings for K2? I'm not seeing anything.
Gantry 5 themes has:
production mode "no" (we've tried this set both ways and it doesn't seem to affect the problem)
asset timestamps: "Yes" - don't know if that is a factor
timestamp period: 0
Not sure if there's anything else I should be looking at? Thank you for taking time to respond. Hopefully this is just a setting that I've overlooked somewhere.

Joomla's global config cache setting is set to "OFF - Caching Disabled", not "ON - Conservative Caching, nor "ON - Progressive Caching".
My previous email lists this and all the other cache settings that I'm aware of. Regarding the website URL, are you wanting to look at the back end? I'd prefer not to post credentials on the forum.