Some posts sometimes not accessible

I’ve been using UM for quite some time now, and in general I’m really happy with it. But right now, I’m getting a bit depressed by not finding the cause of a very annoying error.

The last week or so, maybe a bit longer, I get messages from users (with different roles) that cannot acces a post: they log in to the site, are able to read most posts, but cannot read a (recent) post: they are redirected to the default page for non-logged in users. It’s not always the same post they cannot open.

I’ve checked some of the posts that were reported: settings (author, category ect.) are identical, so I cannot think of any reason why the post would remain inaccessible. I’ve tried changing the UM-settings per page to ‘accessible to logged in user only’ (although that is the standard setting), and at first it looked like that solved the problem, but now I’m encountering the same problem myself.

A post (dated june 24) that I had accessed before, and even commented to, now remains inaccessible to me as admin (that is: on the front end; I can edit on the backend). I’ve tried everything I could think of, but there seems no way I can give myself acces to this post on the front end. In my view, that should never happen to an admin.

When I log in as a regular user (I us a test account for this kind of things), I don’t have any problems with this specific post. This post is not the same as the posts I had complaints about from other users.

I really have no clue what could cause this problem that seems quite illogical to me. I really hope someone can help me on this!
I use WordPress 4.9.7 and UM 2.0.21.

The page I need help with: [log in to see the link]