it should be possible to make a right klick in the area somewhere right of the loop range bar. Then it should also be resizeble by mouse drag again. Could also help to zoom in the arranger.
also having issues with this bar it has shrunk to the left hand side of the arranger and will not expand have tried the advice given here but have had no luck fixing it any further advice would be gratefully received
If anyone else comes here and needs a fix, you can now either press the magnifying glass icon at the bottom right of the workspace next to where it says MIDI or if that's not there (depending on the update) there will be a double ended arrow where the zoom buttons are at the bottom right of the workspace next to the slider.