Issue with USA Counties (admin=6)
When downloading the counties of the United States (admin_level=6), one county in Arkansas (Lincoln County) is routinely absent from the downloaded file. All other counties in the US download OK. I also see that Lincoln County, AR is missing from the drop-down list on the side (under United States and Arkansas). It appears that the admin_level is coded correctly for the county in OSM. Any idea what is happening?
It sounds like you are using a database version from when OpenStreetMap was broken regarding that polygon. Stitch database to one that has the data.
OSM-Boundaries is just an abstraction layer on top of OSM. If OSM data is broken, then it will be broken here as well. OSM is always broken somewhere.