Cannot edit node contents


Editing node contents on my testsystem (Linux-Debian, Apache, PHP 7.2) works just fine. However, after transfering the complete directory tree and MySQL database to the production system on my shared-hosting provider, I cannot change content on THAT system anymore. The little “pencil in a circle” widget is displayed as usual. Also, I can open the content alright using the admin-content-menu. The database (MySQL 5.7) is obviously accessible both from the Drupal (8.6.4) server system and also from my local MySQL-client. 

There is yet another problem on the production system: I doesn’t find images, but displays the “alternate” text, even though they are supposedly in the correct directory. Drupal runs in a subdirectory “drupal” of the domain, which is specified in .htaccess (RewriteBase /drupal) . 

I wonder what I am  doing incorrectly. Any ideas? 
Regards H. Stoellinger

Drupal version: