Thanks for the information.
Do you use the latest version 4.15?
Any chance to repeat the issue according to the step by step description?

Known issues:
1) ‘Themes’ and ‘Customize’ menu items of ‘Appeance’ menu are not shown at the list of menu items to block and as the result they leave unblocked. It was fixed in the upcoming version 4.15.1
2) Corresponding front end top bar admin menu items is not blocked. I plan to fully hide it for roles which has blocked menu items.