You are probably looking some of many channels Telegram listed here, that Telegram is not showing the preview at all, even on third channels created to fix such 💩 issue!

Laws https://t.me/s/LawsTelegram to https://t.me/s/GoogleIndexMe

Human Rights https://t.me/s/HumanRightsChecklist to https://t.me/s/GoogleIndexMe3

Ethical Dilemma https://t.me/s/EthicalDilemmaHumanRights to https://t.me/s/GoogleIndexMe2 (coming soon)

Women Rights https://t.me/s/WomenRightsTelegram to https://t.me/s/GoogleIndexMe4

Rape https://t.me/s/RapeTelegram to https://t.me/s/GoogleIndexMe5 (coming soon)

Suicide https://t.me/s/SuicideRape to https://t.me/s/GoogleIndexMe7 (coming soon)

Stupro https://t.me/s/StuproFatti

Death Penalty https://t.me/s/RapeDeathPenalty

Our values https://t.me/s/WeAreTheFutureTelegram to https://t.me/s/GoogleIndexMe6

Just A SHAME Telegram! Most important channels worldwide simply with this shit!

While Telegram is prefer to show preview of Telegram channels about porn, spam, terrorism, rape (but not facts!), illegality, etc.

Again, would be time you BAN SUCH CHANNELS, exactly like we requested you MULTIME TIMES!
https://t.me/BanTelegramChannels

Do your job Pavel Durov once at all!