Symptom

There are no estimation statistics visible on the story map

Cause

There are two major reasons this may be occcurring:

The affected board is a Kanban board. Estimates are not available on the Kanban board at present. There is an open feature request on the JIRA Software backlog for this functionality: JSW-7265. I encourage you to vote and comment to show your support for that feature.
Projects associated with a multi-project story map use different estimation types. We are unable to calculate or "roll-up" estimates to the Epic level and have chosen to leave them offf the story map to prevent confusion.