This page contains the following error: error on XML sitemap
XML sitemap and feed not accessible on WordPress installation
Error in XML sitemap ->
This page contains the following error: error on line 1 at column # XML or text declaration not at start of entity
This page contains the following error: error on line 1 at column # XML declaration allowed only at the start of the document
Error in WordPress feed->
This No error but unable to see the feed content and if open the feed in chrome i can see some space in front of first line
if you do some research on google then you will get to know that this is something related to white space in some of php file , may be functions.php or wp-config.php or some other file.
1> First try to find/recall If there is any file recently modified by you and if yes then i would recommend that download the file and then check whitespace at first or last line (before <?php or at the end of file) and just remove that whitespace. if you are using FTP / SFTP to modify file then there are chances that it will add the whitespace while modifying file and the same thing happened with me while modifying wp-config.php and the ftp client automatically added whitespace at the first line.
2> if you dont have any white space in recently updated files then try to disable recently installed phugins or if that is not working then disable all plugin and theme and check the issue. you may use conflict check to identify the root cause. Once you have identified whether your theme or a plugin causes the issue, please contact the developers of the theme or plugin for assistance finding and removing the whitespace.
3> if you dont know or unable to find cause but you know that the site was working earlier then use backup to restore wordpress files (not Database) from the backup to correct the files. make sure that you have backup of latest wordpress file and db before you restore anything.