Looks like you're in a small and brief experiment (.3% of viewers for a few weeks) so you're seeing auto-generated thumbnails instead of custom thumbs. This is part of an effort to test/improve auto-generated thumbnails for the many creators that use them: https://goo.gl/A7oDmr
YouTube has gone downhill drastically. You guys made a mistake, and striked me a few times. Shit got resolved, yet you guys haven't said sorry once, for killing an extremely big growth. We were heading to 100k subscribers, and you fucked it up. Shame on you