A few days I try to upgrade a site with Drupal 7 to Backdrop 1.9.0, I have done it many times and always occurs the same problem - the site is upgraded, but Administration menu is corrupted. Dislocated items, absent items.
/admin/content is not available at all - it is impossible to see content list.
I follow literally the instructions here:
(It seems that one step there is missing - before "6. Navigate to this site in a browser, and visit /update.php to proceed with the update." it was necessary for me change in settings file $settings['update_free_access'] = TRUE;)
I remembered that some time ago - beginning of last year - I have done a successful upgrade from Drupal 7 to the earlier versions of Backdrop.
So I went back and did the upgrade procedure again, but to Backdrop 1.2.3.
The upgrade has become successful and now there are no problems with Administration menu.
After that I made an update to Backdrop 1.9.0. Now the upgraded site looks and works fine.
So I think there's a problem with the upgrade from Drupal 7 to Backdrop 1.9.0.
Sorry, I didn't make screenshots.
This step is only required if 1) you were not logged in to your Drupal site, or 2) you were logged in, but did not have permission to run updates. If you are both logged in and have the appropriate permissions, setting this flag is not required. However, thanks to your feedback, we have added this information to the upgrading instructions: https://backdropcms.org/upgrade-from-drupal.
Thanks for working through the update and finding a solution to the problem. I'm afraid we still don't understand exactly what was wrong with 1.9 in the first place, however. Would you be willing to create an issue at https://github.com/backdrop/backdrop-issues/issues, stating what had been done to your menu in Drupal 7, so we can reproduce the problem you experienced with the upgrade?