
Hi @Athanasios Sersemis,
Hope you are doing well.
Problem 1: "Shared with Us" Space Not Working
Concerning the issue you mentioned, we have also done some internal research and found that we would encounter the same situation. We would like to make sincere apology for the inconvenience caused.
Currently, the best way to troubleshoot this issue further is to report it to the related team who has higher permission to investigate this issue from back end, collect the background logs and help you find the root cause.
In this situation, I sincerely recommend that your Microsoft 365 admin, can follow the steps in this article and create a support ticket to contact online support.
Problem 2: Circular Dependency Error in a Specific SharePoint Site
Unfortunately, there is no information about this error to be found in the forums, so it seems to be a very occasional problem. Since this issue only affects specific sites, I would suggest that you create a new site and re-share the files. It's likely that there was some sort of problem with the original site's backend.
If you have any concerns or questions, please do not hesitate to reach me.