I'm starting a new project that consists in migrating an old CMS to a new CMS. The new CMS it is not Drupal, but all content are delivered via API, the page structure too. The page structure is a Json file with a set of entries that contains the name of the block and the parameters.
We use Drupal for the site of our company. It's a great tool!
But we encountered a problem to update Drupal.
Currently the version of Drupal is 8.5.6.
We tried to migrate to 8.6, without success.
So we tried to update to version 8.5.8 (for the security update). The update is going well but it is no longer possible to create or modify a content.
Below is the error message that appears after clicking the "save" button.
I have my source code in AWS Server (Primary & Secondary with load balance and domain pointed to load balance IP address), Database connected to RDS. If I clear the cache, theme is not coming up . it looks like site broken up and if i restore the backup it is working fine. Please advise.