I have heard that a lot of people got their account banned due to unknown reason.
[/quote]If their accounts were banned, Telegram will show reasons of bans for them.
Telegram has hundreds of millions of users. Unless you heard from a few million, at least, you can't say that a lot of people got their accounts banned. 
It's true that changes were made to Telegram's TOS and Privacy Policy
Changes in Telegram's ToS and Privacy Policy won't cause your Telegram account to be banned if you did not use it for scamming or bad things in the past. It's true that changes were made to Telegram's TOS and Privacy PolicyTelegram is a paradise for impersonators, scammers so it's good if these accounts got massive bans from Telegram.