After upgrading to CiviCRM 5.27 (and now, to 5.28) on Drupal 7, I see this warning message.

As you can see, GROUP is listed as "-" (minus). 


[![enter image description here][1]][1]


When I try to click on settings (Gear icon), it shows me Group Settings empty fields:

[![enter image description here][2]][2]


When I click on *Contacts in this Group* (in Group Settings), it shows me all contacts in my CiviCRM database along with some notice warning (a lot of lines exactly like these - Undefined property and Undefined Index):

[![enter image description here][3]][3]

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# UPDATE 
(January, 2021)
The problem is still there after update to 5.33.2. What can I do about that?

[![enter image description here][4]][4]


  [1]: https://i.sstatic.net/mP5p3.png
  [2]: https://i.sstatic.net/zwpon.png
  [3]: https://i.sstatic.net/SGbx8.png
  [4]: https://i.sstatic.net/DZuYc.png