can't move a clip along the timeline

Hi there,

I can't move clips along the timeline - but I can move a clip from one track to another. But the
same timeline. This happens when I work on my MacBook Pro (some keys were damaged
by liquid; I use an external keyboard and blue tooth-linked mouse).

When I edit the same video project on PC - I work normally and do not have this problem.

BTW: The same happens when I use Adobe Premiere.

Any ideas about what's wrong with moving the clips on MacBook? What can I do to make it
work correctly?

Many thanks!