Widget bug: "The '...' block was affected by errors and may not function properly"
Just purchased the ClassiPress theme yesterday. Widget bug. Dashboard>Appearance>Widgets shows 14 pink error messages starting with "The 'nav-menu' block was affected by errors and may not function properly. Check the developer tools for more details." The other 13 pink error messages state the same thing but identify a different block. For example, "search" block, "recent-posts" block, "text" block, etc. Beneath are several widget boxes. All say "Legacy Widget - Widget is missing."
How do I fix this?