Gutenberg editor page attribute (parent page selection) fails when Democracy plugin is enabled

Gutenberg editor page attribute (parent page selection) fails when Democracy plugin is enabled

As soon as I enable the democracy plugin (5.5.6.3) on my wordpress 5.3.2 installation, the page attribute selection where I could select the parent page does not load anymore. When the plugin is deactivated, it's working again.
There is a javascript error:

Uncaught (in promise) SyntaxError: Unexpected token < in JSON at position 0 # data.min.js?ver=4.9.2:1