When running update.php on version 1.28 of media wiki the following error message occurs:
Your composer.lock file is up to date with current dependencies!
Going to run database updates for my_wiki
Depending on the size of your database this may take a while!
Abort with control-c in the next five seconds (skip this countdown with --quick) ... 0
PHP Fatal error: Class 'FormatJson' not found in /var/www/html/mediawiki/feedback/includes/exception/MWExceptionHandler.php on line 624
Hi @Sorvis, thanks for taking the time to report this!
How is this related to the Hitcounters extension?
I'm not sure what the issue is but another user reported the same error who uses HitCounter https://www.mediawiki.org/wiki/Extension_talk:HitCounters#Installing_on_1.28
When I disabled HitCounter then ran the Update.php it ran fine then as well. Its confusing what FormatJson has to do with that though.
I believe this was fixed in dfc16883980d. Please re-test this by installing that version manually or trying the 1.29 or master branches.