App Store doesn't find the Apps I search for

Since upgrading to IOS 9.3.1, when I search for Apps via the App Store they are not listed as being available to install.

If I search for 'dropbox', for example, I get the following:

It doesn't make any difference whether I choose iPad only or iPhone only (by the way there doesn't seem to be a way to list Apps which work on both iPads and iPhones). This problem is occurring on several of my Company's iPads and many of the Apps we commonly install on our iPads are affected by this problem.

The only way I can find and install the Apps I need, is to search for them via Safari then click the Install button in the Google search results.

Can anyone help please?