I ran into this a few times too – not easily reproducible, but such a showstopper that unfortunately I had to move on to a different solution. This addon is not reliable enough, and it’s usually unclear why it’s misbehaving.
Deactivating the plugin is the only way to get it back reliably. Does not matter if you turn off Dynamic Visibility altogether for a given widget (in my case a Container), or toggle the visibility condition (it shows up in the Elementor editor just fine, just not the frontend), it refuses to come back and going to previous revisions of the page (from before the change) does not fix it either. It’s like the plugin gets stuck.