After updating an installation from eZ Publish 4.5 to 5.4, non-breaking spaces in existing contents are displayed in the frontend as " ".
This was a non-issue In legacy as the frontend still displayed spaces correctly, however it can be verified using 5.x / twig

Re-publishing them manually resolves the problem, however this is not possible to do on the whole database.

Note:
The way that nb spaces were saved to DB appears to have been fixed in EZP-18220, however no update script was provided.
A valid solution to this issue would be an update script to update all the contents without manual interaction.

Steps to reproduce:

1. Create an xml text content with the following (as it was stored to DB in eZP < 4.5):

   <?xml version="1.0" encoding="utf-8"?>
   <section xmlns:image="http://ez.no/namespaces/ezpublish3/image/" xmlns:xhtml="http://ez.no/namespaces/ezpublish3/xhtml/" xmlns:custom="http://ez.no/namespaces/ezpublish3/custom/">
   <paragraph>new&amp;nbsp;article&amp;nbsp;test</paragraph>
   </section>
   

2. Verify the content is not displayed correctly in frontend
3. (optional) verify the content is displayed correctly in legacy mode