I just got done reading over the past couple of hours, and it seems this isn’t uncommon and stems back to earlier releases of WordPress. Disabling all plugins, setting a tag and category base, all of those suggestions did not resolve this issue. Unless the default permalink structure is used, 404 errors occur on /wp-admin/ (only there from what I’ve seen thus far). So this is not a mod_rewrite issue, it is evidently a bug within WordPress. Is there any update?