Samsung S4 Mini - problems with whatsapp.

This device was released in 2013, running Android 4.4.2....
I'm thinking whatsapp is updated to run on a higher version of Android, which is causing the problems.
Your best bet is to upgrade your device that runs a newer version of Android to resolve the issue.
IMO, buy an android device that's running Android 11, at least.
That way you'll have a device that will last a few years and that can handle apps made to run on current Android versions

 

or try older apk versions of the app.

but i agree upgrading your phone is your better option. that android os is so old that a lot of apps will not work anymore or you will run into issues like you are having. getting a new phone will solve all such issues.

 

At the moment WhatsApp says it supports Android 4.1 upwards, though I expect that just means "is compatible with the SDK versions used in Android 4.1+" rather than actually tested on devices that still run those OS versions.

It's possible that the s4 Mini simply doesn't have the resources to run the app well. It's impossible to give a definite answer just from a few words of description, but what you describe could be caused by poor connection (e.g. the phone having weaker reception than your handset) or by the phone just not having the processor or RAM resources needed to keep up with the demands of running the app. Maybe voice calls would work better than video (less bandwidth and less processing needed)?