The Sprint Marker Migration described at https://confluence.atlassian.com/display/AGILE/Sprint+Marker+Migration has an error when it recognizes whether there are Boards that need migration.

We had a Scrumboard that matches the criteria

(SPRINT_MARKERS_MIGRATED <> true or SPRINT_MARKERS_MIGRATED is null) and SPRINTS_ENABLED = true

but the board was deleted.

So there was no way to get the warning away except of hiding it which is bad as you then are not sure whether all boards that need migration are actually migrated. (Besides it would be handy to see the list of boards that still need migration, at least as Administrator if there are security concerns.)

I worked around this by setting sprints_enabled to false in the database directly. After this the message was gone as it was the last board that Agile thought needs migration.