I have two websites running on same codebase using multi-site. Two instances (one dev, one prod) experienced the same problem when upgrading security update from 8.8.4 to 8.8.6. The main site update.php works fine, the second site (even if I try to run update.php first on it) fails with error:
The website encountered an unexpected error. Please try again later.
Drupal\Core\Extension\Exception\UnknownExtensionException: The module config_update does not exist. in Drupal\Core\Extension\ExtensionList->get() (line 265 of core/lib/Drupal/Core/Extension/ExtensionList.php).
Drupal\Core\Extension\ExtensionList->get('config_update') (Line: 579)
Drupal\Core\Extension\ExtensionList->checkIncompatibility('config_update') (Line: 318)
update_get_update_list() (Line: 272)
Drupal\system\Controller\DbUpdateController->selection(Object) (Line: 163)
Drupal\system\Controller\DbUpdateController->handle('selection', Object)
call_user_func_array(Array, Array) (Line: 115)
Drupal\Core\Update\UpdateKernel->handleRaw(Object) (Line: 76)
Drupal\Core\Update\UpdateKernel->handle(Object) (Line: 28)
Closed: cannot reproduce
9.5
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
I am reluctant to close issues relating to update but no further information has been provided that will allow us to investigate. Therefor, I am closing.
If you are experiencing this problem on a supported version of Drupal reopen the issue, by setting the status to 'Active', and provide complete steps to reproduce the issue → (starting from "Install Drupal core").
Thanks!