See SponsorBlock disabled (how it should be):

When SponsorBlock is enabled:

How to reproduce? Check on Chrome latest stable version and check out any YouTube video.
I encountered it on: https://www.youtube.com/watch?v=-lYeJeQ11OI&list=PLfllocyHVgsRwLkTAhG0E-2QxCf-ozBkk (a playlist)
I haven't tested any other browser yet. If YouTube has changed some CSS or design then this might be the case on all browsers too