At a glance I thought that was my contribution to the research into it. I'd forgotten this. (long long hours for years on Quora seems to be absorbing my brain.)
I watch a lot of lectures via YouTube and I think, but not totally sure, PPRuNe is the only site that blanks them out.
I've just fired up my SONY VAIO i7 running W7* and it too fails to show the YouTube.
*Went back to W7 when Sony had no W10 drivers for this laptop. SONY told me that a group of investors had bought the VAIO name and SONY were not interested in wasting resources for a unit that had just missed their support for W10. The buttons supported by drivers were too handy to forgo but W7 is probably the reason it had been unused since November. Shame.