After Update to 8.5.6, "Add" Links Missing From Page but still are in router I recently manually updated Drupal to the 8.5.6 version.  I did this by moveing over the files (using command line) according to Drupal.org instructions and running update.php.

I have two issues that I'm guessing are related:


My themes no longer toggle from the front end and I can't force them to change by clearing cache, running cron, rebuilding menu or anything else that I can think of.
All "add" links are missing ** - "Node/add" is present in the routing file and still works.  However, it is missing from the content page. It also seems that ALL "add" links are missing from the site. To get there, I need to manually type in the path.


I am running out of obvious ideas on how to fix.  Can anyone point me in the right direction?

I followed the instructions below: 

Drupal Page on Running Installation Manually

Below, you can see the commands Drupal tells you to follow:

cd /path/to/your/drupal/directory
rm -rf core vendor
rm -f *.* .[a-z]*
wget https://www.drupal.org/files/projects/drupal-x.y.z.tar.gz
tar -zxvf drupal-x.y.z.tar.gz
cd drupal-x.y.z
cp -R core vendor /path/to/your/drupal/directory
cp *.* .[a-z]* /path/to/your/drupal/directory
Thank you everyone for your feedback. 

We ended up wiping the whole server and starting over.  I had done various updates manually by dragging and dropping. We re-installed Drupal and this time around used composer and drush.  That solved the issue. I was not able to ever FINALLY diagnose what happened.