for me it also was connected with the themes. 

Solution:

Go to the developer mode ?debug=assets then the page is working again - in the frontend install a different/new theme. Then it also works without debug mode.

And there was an issue with caching.

If I deleted the assets in the database they got regenerated and then it worked again.
res = env['ir.attachment'].search([('url', 'like', '/web/%')])

res.unlink()

   I had the same problem, it seems that the theme gets unlinked when the restore takes place, so what I did was to change or reselect the web site  theme and it worked. 

Hi.

All i did was restore a database from one pc on to another pc and then this error popped up. everything is identical. so i am not sure

If you have custom modules or custom themes, they could be causing the compilation failure. Review any custom CSS, LESS, or SCSS code for syntax errors or compatibility issues.

Temporarily disable custom modules or themes and restart the server to see if the issue persists.

Hello, Please make sure you have installed libsass==0.20.1 library.