After clicking on an artist name (for ex), using the Page Up/Down keys has no effect. It's only after clicking on a song that the keys become active. For easy navigation it would be good that the keys have an effect on the current page at every possible stage, in every possible situation.
We tried reproducing this on our side and when using the keys on an Artist page it's not necessary to have a track clicked. In such a case we recommend performing a clean reinstall of the Spotify app on your device to see if this makes a difference.
If you see no difference after the clean reinstall, check your hosts file for entries that need to be deleted. Follow the steps described here on how you can do that.
Let us know how you get on! We'll be here in case you need any further help with this.