iPhone asks for Apple ID password on third party app launch after iTunes sync

I've just synced my iPhone with iTunes to get some Music on the iPhone. After doing so, the iPhone wants my Apple ID password, when I try to launch a third party app. All Apple apps (Photos, Safari, Notes, etc.) work fine, but all third party apps require me to sign in to the App Store first. I mean once; as soon as I signed in once to the App Store, all third party apps start to work again.

On my iPhone I use the same Apple ID as in iTunes.

This is the popup when I'm not connected to the internet:

By the way, this is by far not the first launch of "FBReader".

And when I'm connected to the internet it looks like this:

I can't even do this on the iPhone, because my password manager doesn't work of course! I need internet and a second device to get my iPhone working again.

Is this expected, normal behavior? Is every Apple user suffering this?

Or is there something fishy on my device(s)? I suspect that this is a copyright mechanism that runs amok because the iTunes sync cripples my iPhone.

Some time ago, I've changed the Email address of my Apple ID. Before that, this never happened. However, this was some time back and since then many updates to both my iPhone as well as my Mac happened.

I can't answer the part about if what is going on is fishy but I have a similar experience when I log in iTunes with a DIFFERENT account than my phone but this is apparently not your case. As far as the second part of the question no this does not happen to everyone.