Users of Telegram Messengers in certain parts of the world had trouble exchanging messages through the service today. The problems were caused by a distributed denial-of-service attack aiming at Telegram servers. The service outage affected users mainly in South and North America, although connection issues were present in other parts of world as well. The hot spots for the DDoS attack were on the East Coast of the Americas, in the United Kingdom, the Netherlands, Germany, Ukraine, Russia, and China. The situation is stable and users should no longer experience issues when using the Telegram messaging service.
Source: https://www.bleepingcomputer.com/news/security/ddos-attack-on-telegram-messenger-leaves-users-hanging/