Can't open/create new mind map / "refused to connect"

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Nextcloud version 15.0.7
Operating system and version _CENTOS 7
Apache or nginx version httpd-2.4.6-89.el7.centos.x86_64
PHP version PHP 7.2.18
MindMap version 0.0.13

The issue you are facing:
I cannot create nor access an existing mindmap anymore.
In firefox I get a blan screen when trying to access the mindmap file. In Google it opens a blank page at first and then says www. refused to connect

It used to work fine. The only thingthat has changed is that I have a new laptop (CENTOS 7 Desktop as before). Am I missing an extension ?

Is this the first time you’ve seen this error? (Y/N):

Steps to replicate it:

  1. Open existing mindmap
  2. Crete a new mindmap (

Thanks for any hint to fix this.