Force to downgrade after upgrade to Drupal 8.4


I had upgraded to Drupal 8.4 but then realized my theme was not compatible with that version and was forced to downgrade back to 8.3.7 for the time being.

I was having some issues with Mismatch entity issues and I found posts in forums suggesting uninstalling modules that were related to the issue. I therefore uninstalled the Blocks module, used drush entup to fix the issue and reinstalled Blocks again. However, now I lost all the links, tabs, titles and breadcrumbs in the backend/admin pages.

Where can I change how the backend theme looks like or what is displayed?

Sorry if this is in the wrong category/section of forums.

Thanks in advance.

Drupal version: