I am not a developer or technical but I have seen similar 'code' in the Restrict access field when there has been a particular contributed plugin that is not compatible or set up correctly. What's strange though is that I would expect that to be the case for all teachers in the same course but you are saying other teachers in the same course can use Restrict access but one teacher cannot. Do they all have the same permissions -and can you check any plugins used in the course/site which might be out of date?