ubuntu 18.04 workspace selector not properly rendered

[aldo3]

I recently updated my (gnome) Ubuntu from 17.04 to 18.04 and I got some problem with the workspace selector, the one shown at the same time (but on the opposite site) of the dock. It takes always the same size, independently from how many workspaces I selected but, more importantly, the highlighting border is almost always off-place and doesn't move. Here I am attaching a (link to a) picture:

https://i.stack.imgur.com/kDp0a.jpg


Does anyone experience the same issue? Do you know of a way to fix it? I tried to change the number of workspaces but that is not able to trigger an "update" of the selector.

Thanks, bye
Aldo