The default display settings for the SETTINGS > SYSTEM > Apps & Features page are to display apps "By Size" and to look for apps on "All Drives". The latter is particularly stupid when you consider that Windows and the Store app install all apps to the This PC (aka the C: drive) by default.

In my case I have three drives, two of them moderately large (1 TB) and one of the 1TB drives is compressed. So every time I exit the Settings app and come back to it the Apps & Features page has to go out and search all drives for anything that looks like an app or feature before it will allow you to do anything. In my case it takes nearly 10 minutes before it's ready to do anything.

The most maddening part of this is that the display settings for the Apps & Features page are not sticky so you can never change the default behaviour to something more sensible like search for apps only on "This PC" (one of the selections available) instead of "All Drives".