Seems like a common theme online. Know that power saving mode only really allows essential apps to work fully. So things like messaging and phone will work fully but other apps like Instagram will not fully work properly. It is why you put power saving mode on, to save well, power. Get out of power saving mode and then try the app. Odds are it's power saving mode, saving you power. If you are not in power saving mode then that is odd. I tested Instagram just now and uninstalled and installed the app with no issues. Even checked settings in the app, there really are no settings.
Only other thing I can think of is what connections you all are using. Is it wifi with a weak signal? Is it phone data with a weak signal? If in data mode try wifi.