UI Builder scripts not working after restarting Unity

Hello,

I am using UI Builder for my project, and I've got an issue where, after I re-open my project, the script inside of UI Document (in other words, its component script) stops working. ¨ this is what Unity tells me:

to make this work, I have to delete the component, delete the script and create an identical script (it works even if it has the same name as the previous one).

if I only delete the component, and try to re-attach the same script, I get this error:

it tells me to check compile errors, however there are not any. And to check if the class name matches is the file name, which it does.

I am really at a loss here, dont know how to solve it, at all.