You may have noticed some service interruptions between July, 10–12. This was due to a sophisticated DDoS on Telegram's Asia Pacific cluster. You can read more about it in this post:

We were able to quickly restore ordinary service for all users, except mainland China. Unfortunately, it seems that the Chinese government is now at least partially blocking Telegram after labelling it as an "anti-government" tool used by human rights advocates for encrypted communication (the block coincided with the DDoS).

For the rest of Asia Pacific, Telegram messages are back on track since July, 13. Sorry for any incovenience caused by the DDoS. Please contact Telegram support if you have any lingering issues (Settings — Ask a question).

중국에서는 대놓고 텔레그램을 막는가보군요. 뭐 ... 이래저래 동아시아 전체가 다 이상하게 돌아가는 것 같습니다.