Its not a rumour, they have been told so by Aer Lingus.
Following info from Travel Weekly.
Stobart Air has been told that it will no longer run regional services for Aer Lingus.
The Irish carrier informed parent company and Southend airport owner Stobart Group that Stobert Air is not the preferred supplier for a new commercial deal which would have started in January 2023.
Stobart Air will continue to operate the Aer Lingus franchise until that time.