@TeamYouTube The YouTube Android app is also gettin' nuts. Apparently when you searched somethin', it just agressively and unconsistently caches the thumbnails of the last searched videos. This whole auto-generating thumbnail experiment is the one that caused it, I presume.
But @TeamYouTube, please... research and test more Android phones, because some of their OS could also cause a problem or an incompatibility issue. Please do that so that I and perhaps others won't get too lost with only 1 non-specific fix.