@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.
Yes, it did worked out in the end, the problems are lying beneath my phone and the YouTube app itself. After fiddling around with the Play Store and YouTube data, and by using an apk, I was managed to get it up and running again.