Ranking is disabled, as the Filter Query for this board is not ordered by ascending Rank.

[koteswararao]

we had a sprint planning this morning but we cannot reprioritize epics or user stories and tasks (it is also blocked in user story mapping and I obtain the following error message);

Ranking is disabled, as the Filter Query for this board is not ordered by ascending Rank. Please check your filter configuration.

[Nic Brough -Adaptavist-]

You need to do what the message says - change the board filter back to having "order by rank" as the only ordering clause.

[KevinP]

Posting this here for posterity.

I had this error in a Teams-managed Roadmap, which had no filters applied. Creating new filters etc, had absolutely no impact, the error persisted. 

The fix in our instance was fairly simple: someone had created a new custom field named "Rank". Renaming this field to "Service Desk Rank" resolved the issue immediately.