pickerFieldUsersAndGroups not fetching the group name on the basis group id provided in the DB

Do you store the string "[Group: 77]" in the DB? Why? You only need the ID. 77 in this case.

Sure, that picker field takes the ID directly.

Just like Stefan mentioned , Can we know how it stored in DB (Structure of Fv!item) .I assume it's not stored with those square brackets (You might have confused with the Raw output value). If it's stored in this format i suggest on changing it 

Extract will return the LIST, can you try indexing?