Hi Zofia-
Since Flothemes are commercial themes, we haven’t tested the BoldGrid Post and Page Builder with that theme. Since you mentioned that it includes its own blocks and elements, it’s possible that they’re not compatible. First, try disabling the Post and Page Builder and Post and Page Builder Premium plugins, and see if that lets you save your layout sections.
If you’re still having trouble, I’d recommend reaching out to Flothemes Support for more information.
We also have a detailed guide with a video tutorial on how to create a menu with links to different sections of a page, otherwise known as “Anchor Links.”