Disabled workspace switcher on second monitor in Ubuntu 18.04

I’ve updated Ubuntu 18.04 from Ubuntu Gnome 16.04. On second monitor I see a workspace switcher on the right side, but it is always closed and does not react to any actions

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In Ubuntu Gnome 16.04 it always opened and you can easily switch between workspaces and drop apps.

“Workspaces only on primary” is disabled.

How can I fix that?

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