I ran into this same issue. It happened when customizing the Astra theme and going to Global > Blocks Editor and changing the “Core Blocks Spacing” to any setting other than Legacy.
The issue was fixed by enabling the Improved Spectra Compatibility – see steps below (also ensure your plugins and theme are updated to the latest version):
https://wpastra.com/docs/improved-spectra-compatibility/
The fix above should allow you to avoid having to add custom CSS.
Eric
