Seems to have started tonight.
It's fine here. iOS 12.3.1, iPad Air 2. Both AU and IAA versions load fine.
It would be sensible to post some details such as iOS version, device, whether this is a new project or an existing one, and more about the reproducible steps you take and the behavior you see when it doesn't initiate.
And, it should go without saying, but ... have you tried shutting down and restarting the iPad?
Also, another thread reminded me - if apps are "offloaded" to save storage (see settings > storage), they still show up as available, but do nothing when you try to launch them from within other apps.
Restart your ipad @The_Bro
If the issue continues, post your ipad model and ios version.
Also check for updates in the appstore.