so browser issue not ISP for some?
On my laptop, YouTube videos would fail to play properly on my BigPipe connection, but work on Spark.
It may be different for others, but given DarkShadow's tip-off, from my point of view it would appear that there's something going on in BigPipe's network that's interfering with QUIC connections to YouTube. No idea about BigPipe's internals... Firewall configuration? Caching? If QUIC-enabled browsers are redirected to different Google servers, perhaps even routing?