Error after update to Joomla 3.9

[pklinke]

The error still exists after 2.0.12

Ungültige Backend Antwort.
Daten nicht im JSON Format.

[asika32764]

Tested in Joomla 3.9 without any issue.

Please check if toolbar.php message still exists, it means you haven't install ARI 2.0.12 successfully.

If there has no toolbar.php message, but still shows JSON format error, it may broke by 3rd party plugins, try set error report to none in global config:

[pklinke]

When I change from standard to none the JSON error is gone. No toolbar message.

[pklinke]

I now have removed Remoteimage and new installed: well, no error. Error Reporting stays on Default.
One time open options, "save" without changes and the JSON error occurs again!

This I can reproduce every time.

Isn't there a solution?

[asika32764]

I cannot reproduce this issue with the steps you provided.

Could you please install Remoteimage in a clear new Joomla instance to test it?