After a stepdown, the new balancer is not fully aware of the migrations created by the previous instance of the balancer. This can produce that a stopBalancer command is not able to ensure that migrations generated by previous instances of the balancer are correctly stopped.

The design of the solution has to consider situations where the source of the running migration is directly or indirectly issued by the user, instead of automatically generated by the previous instance of the balancer.

For user scenarios, the functionality is not expected to happen often, and does not seem to have a significant impact in the user experience. In the tests, we had to introduce some workarounds in stepdown suites to workaround this problem (see SERVER-85441 check_routing_table_consistency_helpers.js)