Open Associated Grid button disappeared

Hi guys,

We have an issue on Marketing List form. The Open Associated Grid View button disappeared for contacts members grid. For accounts and leads the button is present.
I've checked the command bar (using Ribbon Workbench) and there are no modifications at all for contacts. Also I've found https://community.dynamics.com/crm/f/117/t/122218 article, but there is no Contacts connection on Marketing list form as it uses listmember entity. There are no scripts on the form too.

Am I missing something? Have anyone faced this issue before?

CRM version is 8.1, Online.

Any clue would be appreciated.