Thank you for having looked at this @Don! I also thought it’s related to the dynamic header-offset declaration. On the other hand you can change the header to non-sticky here on meta or other instances and it’s no issue. E.g. on this instance I use similar components, but the page doesn’t extend with a non-sticky header: https://community.couchers.org/
So I still wonder why with this other theme. Though I also wonder what the header-offset value is actually calculated and used for?