It's most probably caused by the apps you're using....
That's the big problem with apps, if not coded well, they take up a bunch of resources and slow the site down...
But Shopify doesn't support doing this: https://community.shopify.com/c/Shopify-Discussion/How-to-set-up-browser-caching/m-p/450953
add this snippet ;)
<!-- Leveraging Browser Caching --> <meta http-equiv="Expires" content="30" />
content="custom value of days"
The meta data above means that document is considered expired after the specified date and time. If you set it to “0“, the browser will check for a fresh new document on each visit.
Agree when it comes to app. For simple site tweaks such as top bars, promotional bars, etc, it's best to code them directly onto the theme and not rely on third party apps.