Database upgrade fails updating to CiviCRM 5.22.1 to 5.28.3
The problem with updating to version 5.28 was apparently due to some of my civicrm sites having been originally installed with version 4.7. I edited the settings file by comparing to a version 5 setting file. A critical line (~82) was commented out.
Un-commenting that line (and updating other sections of the setting file) allowed me to update all my sites, both live and on the dev server.
Also note that line 82 may be commented out on sites that were originally installed in the early days of CiviCRM 5.x.