- Migrate tasks sequentially instead of in parallel
- only migrate tasks matching the old key format
- added test to verify that old tasks break migration
- added test to verify already migrated tasks are excluded from migration
Needs to be merged into releasing-0.14 as well.
Note this will only fix the reported subsequent error when trying to migrate already migrated tasks. The underlying problem ist not yet clear, but it might be that the parallel execution of task migrations introduced the problem.