After upgrading to concrete version 8.1.0 my sitemap is empty in dashboard. I can see the complete sitemap when ticking 'show systempages'.

But when having to select a page from the sitemap through the editing interface, for instance for making a link, i'm still getting the empty sitemap. Meaning i have no functionality anymore to link pages...

I've checked al site permissions and as far as i can see those are all ok.
Can someone shine a light on this weird problem?