Currently, if any code tries to access/write data without the relevant permission given to the currently logged in user (or anonymous if you're not logged in), no error is shown in the log file!

I believe this is an extremely common issue coming up to many developers, whether new to Magnolia CMS or advanced.
I had this problem several times in the past few months, on new projects as well as on existing ones. Lately I worked on a migration, after migrating I tested a page & I could not see some of the data. I had to go through, checking the location of the data imported, checking the data itself (export), modifying the template script, & so on, until I found out it simply was a permission issue. It can take a couple of hours to fix/understand, as it is so easy to forget about this possibility.