I have same probelem with two iMac (Catalina 10.15.4)
I attached a CSS file to my blocs project using the project attachment.
When I edit the css (with Visual Studio Code for example) I have to remove the attachment and re-attach it with different name completely for changes in the CSS file to be reflected in Blocs.
I’ve tried to remove and re-install Blocs…
I’ve made a new project…
And I still have same problem.
Seems Blocs cache the external css
Never happened before and It’s making me crazy.