All audio clips on Timeline One are stuck and cannot be moved, lengthened or shortened

The problem: About a year ago I recovered (via OnTrack) a very large project from an earlier Premiere Pro CC version. This project has now been imported to version 2018. Routine, so far. The problem is that all clips on audio Timeline One (there are several audio timelines) seem stuck. However the audio plays back just fine. Individual clips on Timeline One can be deleted via a small work around, by drawing a rectangle via mouse right on that clip and clicking ‘delete’. But the clips cannot be moved, shortened or extended. All clips on Timeline One are locked, but they can be deleted via the above method, which is not at all what is wanted. Regular editing is thus no longer possible on that track. I prepared a set of eight screen captures that document the problem in some detail.

I want to show the problem to the community, hoping for a moderately easy fix, maybe via a screen captured tutorial.