Thank you for clarification. I can reproduce the issue.
There are two workarounds for it.
First one: copy setup-sheet post into your local library.
Open post library:

Open "Fusion Library";
Select "Setup sheet" filter on right side;
And copy "Setup sheet (html)" into your local library.
If you are using Excel setup sheet you can copy it as well.

Fusion will not use setup sheet from local library, so you can immediately delete it. It is just for caching online post.
Another workaround is to use locally installed posts instead of online. But I don't recommend this. To disable online posts library unselect this preference:

Hopefully, it helps.
Sorry for inconvenience.
Viacheslav Shapilov
Developer Technical Services
Autodesk Developer Network