1. Install a regular ezpublish installation with "clean";

2. Follow the steps provided at:
https://doc.ez.no/display/EZP/Installing+eZ+Publish+Legacy+on+top+of+eZ+Platform
and the changes to EzPublishKernel.php at:
https://jira.ez.no/browse/EZP-24109

Afterwards, try to access legacy admin, platformui or simply frontend.
Legacy admin cannot be accessed, so can't platformUI, and sometimes even frontend

After ezpublish.yml has been changed to ezplatform.yml, if one installs ezpublish legacy, it appears we end up with both ezpublish.yml and an ezplatform.yml with repeated settings, and I fear this might have something to do with it.
Not sure even if this is something that at this point should be taken care of.