New answers tagged access-denied
As stated in my last comment: it turned out I didn't publish a certain page layout as a major version. After doing so, the access denied no longer happens.
I've solved it now. The solution was to first give the user group access to the sub site itself. Before I had given the user group the Permisson Level Read - but then they would be able to see all the links in QuickLaunch and go to the site. However, I found there was already an existing Permission Level with very restricted permissions Restricted ...
Instead of giving Full Control permissions on Web give Full Control permissions on the library only.
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