Telegram founder Pavel Durov has said that Apple has been blocking updates for his app; preventing it from being prepared for the iOS 11.4 update that recently arrived. It has also prevented Telegram from complying with the new European Union GDPR.
According to Durov, the problem began when Russia ordered Apple to remove Telegram from the App Store. Mostly due to the fact that it was banned for refusing to hand over private encryption keys that would allow the Kremlin to spy on users. In return, Telegram was banned in Russia in April; resulting in the current App Store block.
Unfortunately, this block has affected all Telegram users. Not just those in Russia. Apple itself has not announced anything about the situation, and is unlikely to comment. Seeing that it rarely says anything about such matters.