A quick look tells me it is a bug related to the content of the Action table: for some reason the Repo field is null for these users, hence the panic. A workaround could just be to remove the content of that table (only for users with the problem) on your experimental instance and check if it helps. Newer entries will likely be populated with non corrupted content.
Don’t hesitate to PM me if you need more help: I provide Gitea services (see the message I posted yesterday on this topic).