Message from particular person is not shown

After setting up a new Exchange Web Services account in EM Client, when I try to read any message from a particular person on the same ornganization’s Exchange server as I am, the EM Client displays orange and black “running line” at the top of message window and doesn’t display the message at all, even if I wait for several minutes. If I then select any other email message, also in other accounts (Gmail) the running line still shows for a couple of minutes, and then finally this other message gets displayed.

If I try to read replies from others to the problematic email message, the same happens. I checked the source of these messages and as it seems nothing strange is in them. They are in HTML format. I’m using EM Client 8.2.1721 (3b3cd99).