Switching keyboard to emoji one when entering caption causes the input field to jitter. It also affects the preview if caption belongs to a video. 

Glitches with video messages – artifacts near the borders, noticeable when the dark theme is set.

When the history is not loaded yet, jumping to the latest message in the chat is sloppy: loading messages are replaced with a progress circle, once loaded messages appear with blinking. It would be more accurate to show the overlaying progress circle until all the messages are loaded (just like it is implemented for clearing cache in settings).

Empty message bubble blinks when a video appears in chat. Blurred preview should be shown instead.

Black screen in player when viewing GIFs which loading is in progress.

Missing channel info when joining channels via invite links. Channel photo and subscribers count should be displayed just like on iOS.

Date box blinks when closing photo in shared media, if that photo is overlapped with the date box.

Not possible to copy hashtags or usernames.

It’s not possible to tap and copy a phone number in Settings. Screenshot from iOS app for example.

It should be possible to tap and hold a sticker in Trending Stickers to open a preview.

Missing feature: it should be possible to open and save GIFs in Instant View pages, just like in regular chats. IV example:  https://metro.co.uk/2016/05/18/8-wonderful-gifs-from-the-last-shadow-puppets-video-miracle-aligner-5890602/).

Missing progress circle when removing or adding users to channels.

Long voice messages duration should have another format. The current format is mmm:ss. The proper one is hh:mm:ss.

Video messages should have auto-play enabled once being sent. Currently they are static before the uploading is completed.

Pulling down the hidden Archive is currently an unpleasant action for users. Wouldn't it be great if the hidden Archive was pulled down with an animation like this?

If app is restarted, there is a delay on keyboard launch when replying to a message while the keyboard is hidden.

The chat photo ('Party Business') blinks, disappears and then reappears.

Boxes in Settings are not animated right now. It would be great to add some animations . Here's an example: