I'm getting the same issues. I don't think this is a Youtube problem, rather a problem with the unit itself since other Chromecast apps are doing this too.
I have the same problem. It affects YOUTUBE (no matter if if play it from Nexus 5, other android rooted or stock, or laptop PC).
It always start and restart the Chromcast. It doesn`t affect all youtube casts, but all with official music video. No matter if material is runing with full HD or lower resolution, but I suppose it happened always when the chromecast automatically change resolution to higher.
My question is, what HDMI standard you have in your TV display?
I have Samsung LE46A756 - It support only HDMI 1.3c.
Could it be related to DHCP, maybe Chromecast restart to protect HDCP content.
Everything work fine when I connect Chromecast to Samsung C27B750X! This is evidently associated with the display!, not with power source, chromecast device, router/network settings, region.
Chromecast with Eureka ROM 14975.002, but problem has started since November.