@TeamYouTube @YTCreators Custom Thumbnails are no longer sticking on my channel. They'll show almost everywhere my end (Studio Beta/Classic) and via links. Sometimes it shows a random thumbnail during edit (not an auto-generated one). Happens since Premieres enabled.
Cleared Cookies/Cache (All Time) for both Firefox and Chrome. Firefox shows correctly on channel for latest published, but current unlisted reverts Custom Thumbnail slot during edit to middle auto-gen thumbnail. Chrome no change, still broken.