Can't "share" a game from its web page onto Twitter

[Phroneris]

Hello for the first time.
What happened to Steam website?

Steps to Reproduce:

1. Login to both Steam and Twitter
   
2. Go to the top page of a product on Steam (e.g. https://store.steampowered.com/app/391540/Undertale/ )
   
3. Push "Share" button on the middle right of the page
   
4. Select Twitter icon in the dialog

Expected Behavior:

• A new tab of tweet composer is opened with pre-populated text containing the game's name and/or URL

Actual Behavior:

• A new tab of Twitter is opened but it says "Sorry, that page doesn't exist!"

Notes:

• Browser: Chrome (latest)
  
• OS: Windows 7, 64-bit
  
• When doing the same on Safari/iPhone, Twitter app opens blank tweet composer.

And, aren't there any ways to report issues/feedback about Steam web interface like this?
I saw the "support" page but its help wizard doesn't seem to have such choice.

[Phroneris]

URL: https://twitter.com/intent/tweet/source=steampowered.com&status=From+%40steam%3A+Steam%EF%BC%9AUndertale+https%3A%2F%2Fstore.steampowered.com%2Fapp%2F391540%2F