I try to follow https://docs.civicrm.org/sysadmin/en/latest/upgrade/wordpress/ to upgrade from 5.25 to 5.28.n as 5.25 is broken in WP5.5
After the step Point your web browser to the following URL
http://example.org/wp-admin/admin.php?page=CiviCRM&q=civicrm/upgrade&reset=1
I consistently get this error despite following the instructions to the letter. I have no extra extensions, on the face of it, this would seem a fairly straightforward process.
#0 /home/customer/www/example.org/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Error.php(337): CRM_Core_Error::backtrace()
#1 /home/customer/www/example.org/public_html/wp-content/plugins/civicrm/civicrm/CRM/Upgrade/Page/Upgrade.php(82): CRM_Core_Error::fatal("Your database has already been upgraded to CiviCRM 5.25.0")
#2 /home/customer/www/example.org/public_html/wp-content/plugins/civicrm/civicrm/CRM/Upgrade/Page/Upgrade.php(57): CRM_Upgrade_Page_Upgrade->runIntro()
#3 /home/customer/www/example.org/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Invoke.php(311): CRM_Upgrade_Page_Upgrade->run((Array:2), NULL)
#4 /home/customer/www/example.org/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Invoke.php(68): CRM_Core_Invoke::runItem((Array:13))
#5 /home/customer/www/example.org/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Invoke.php(36): CRM_Core_Invoke::_invoke((Array:2))
#6 /home/customer/www/staging21.example.org/public_html/wp-content/plugins/civicrm/civicrm.php(1601): CRM_Core_Invoke::invoke((Array:2))
#7 /home/customer/www/staging21.example.org/public_html/wp-includes/class-wp-hook.php(287): CiviCRM_For_WordPress->invoke("")
#8 /home/customer/www/staging21.example.org/public_html/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters("", (Array:1))
#9 /home/customer/www/staging21.example.org/public_html/wp-includes/plugin.php(478): WP_Hook->do_action((Array:1))
#10 /home/customer/www/staging21.example.org/public_html/wp-admin/admin.php(254): do_action("toplevel_page_CiviCRM")
#11 {main}
Warning: Cannot modify header information - headers already sent by (output started at /home/customer/www/example.org/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Error.php:478) in /home/customer/www/staging21.example.org/public_html/wp-admin/admin-header.php on line 9
WordPress 5.5 is available! Please update now.
Sorry, due to an error, we are unable to fulfill your request at the moment. You may want to contact your administrator or service provider with more details about what action you were performing when this occurred.
Your database has already been upgraded to CiviCRM 5.25.0 ```
Any hints welcome... I get this with 5.28.0 and 5.28.3 over past couple of days.