I was not actually sure of what happened, but I had the confirmation yesterday: the Thai government blocked access to Youtube on 9/03.
Youtube was redirected to the page of the Ministry of Information and Communication Technology. However, nobody really knows why it happened, as Youtube isn’t a particular threat to the Kingdom of Thailand.
This is also to remind that censorship in Thailand is (commonly) used by the government. Particularly by the Royal Thai Police, the Ministry of Information and Communications Technology (as mentioned), and the Communications Authority of Thailand.
You can read more on these websites:
11/03 @ 08:03pm