We've been having another issue with posting to facebook of late. As of the 2.11 API update last month, we've had issues posting blogs to Facebook with new apps with our clients.
Once the app is setup and we try pushing a post, this is the error that we receive in the log: https://drive.google.com/file/d/1B7YyFCRd2EOcWODsLTrwMhsf_y2mBYyK/view
The error tells me this has to do with the changes Facebook made to URL editing some months ago, however these shouldn't affect us as we don't edit this information beyond what appears on the site anyways. I've created a user on the site so you can take a look at this, so please let me know if do and what you figure out.