Vladimir,
I found this forum post and it helped me:
I went to my network admin > users > user role editor.
From there I clicked Update Network. It worked!
Just so I understand better.
If I want to make changes to roles, widgets, meta boxes, etc. I should do this from the Network Admin page and use the Update Network button?
I’m confused about the Apply to All Sites button. What does that do and when should I use that?