Since I began using WordPress my website had this weird issue where it would show all my blog posts once you add the feed to an RSS reader but would never show new entries. Also, the official iOS app somehow mixed posts and pages and showed some of them multiple times and the newer ones (the ones I wrote after importing everything into WP) did only occasionally show up in there.
I know, this is like the worst error descriptions ever, but unfortunately I had no chance to figure out what actually went wrong during the setup and import of that new WP site.
So I began asking for help on this in different places to get this sorted out. Unfortunately, my problem description was probably to inaccurate to get valuable feedback. So I tried a few things myself like cleaning up the WP database using WP-Optimize and checking the database manually. Though I was not able to find anything suspicious in there. Damien tried to help me over on StackExchange and we figured out, that the feed issue seems to be gone. I assume, that that has something to do with cleaning up the database since that’s the only thing I tried that was manipulating my data.