Also got the same 500 error on landing pages (upgraded from Mautic 2.16 or newly created in Mautic 3) after upgrading to Mautic 3.0. Editing worked but view/ preview generated errors just like you report. Have rolled back update to v2.16.
Also got the same 500 error on landing pages (upgraded from Mautic 2.16 or newly created in Mautic 3) after upgrading to Mautic 3.0. Editing worked but view/ preview generated errors just like you report. Have rolled back update to v2.16.