Symptoms

Assume the scenario when it is necessary to configure escalations individually for each user from approvers group. This seems not to be possible when approvers group used as a destination set for your approval activity.
 

Diagnoses

While your group approval configured within single activity block all escalation configuration is being done on activity level, meaning that we escalate activity, and though you may send out different escalations to different users they will all fire based on non performing required action on activity for all users. So we counting escalation time for activity not for separate users in such case.

In case when your desired functionality is user level escalations, i.e. something like this:
User 1 approved the task within two days -> No escalation
User 2 didn't action the task within two days -> He should get an email after 2 days and after 3 days the task should be redirected to User 3.
User 3 approved the task within the two days -> No escalation
User 3 didn't action the task from User 2 -> He should get an email after 2 days and after 3 days the task from User 2 should be redirected to User 2

For such scenarios you have to split each user approval into separate activity and configure escalations on activity level. This pose an issue for using group as destination set, at least directly.
You can come up with something like reading single user from group for each separate activity somehow so that you still rely on approvers group as opposed to individual user destination, i.e. destination will be user but pulled from a group, or you just may store your approvers in SQL table, and pull approvers by ID 1-3 for each separate activity. This is an example of one possibility to implement this.
 

Resolution

See Diagnosis section.