Audition April 2019 update build 12.1.0.182 - are you having trouble dropping files into Multitrack view?
Unfortunately there's a bug in this release which was only discovered just before launch date. The situation is that when you right-click in a blank part of a Track in Multitrack view and select Insert/Files, it doesn't work any more. If you select a file in the Import File window that opens, it now just gets added to the Files panel, and not directly onto the Track. In the previous release, it's added to the track, as it should be if you select it from there.
Things you can do: You should have no difficulty in rolling back to the previous version using the CC app, if this is really bugging you.
Alternatively, although not ideal, you can go about the process in a slightly different way: If you have a multitrack session open, you can locate the file you want to add completely outside Audition (i.e. not in the Files window but in its own folder on your machine). Pick it up, and drop it on the timeline. It opens where you drop it, and it's also now present in the Files window.
This should, I hope, be fixed in the next update.

