Hello, Natalia Isupova.
Thanks for reaching out to our Microsoft Community Forum. Please accept our warmest regards and sincerest hope that all is well.
We understand that the Microsoft Loop component in your Outlook for the web app disappeared. And it seems to be happening randomly to your co-workers as well.
Since it happens to you and some of your co-workers, you need to be contacting your company's I.T. department for help since as explained in the links below they have full control on who can access Loop.
Feel free to reply to this thread if you need further clarification or help.
Sincerely,
Glenn Rue
Forum Moderator
Microsoft Community