The site is loading its logo over HTTP instead of HTTPS, leading to mixed-content errors:
From the Chrome console:
Mixed Content: The page at 'https://discourse.metabase.com/' was loaded over HTTPS, but requested an insecure image 'http://discourse.metabase.com/uploads/default/original/2X/0/04a2a02632e6dad26c2709c0b8c821dabd624dd6.png'. This content should also be served over HTTPS.