The sharding_jscore_passthrough_with_config_transition will enable the balancer without setting the corresponding shell global variables (as done here). This can prevent some test from handling correctly a possible moveChunk/moveCollection in the background.

As example, the variable is used by the solution proposed in SERVER-89764 to correctly check the resulted number of bucket documents after timeseries insertions, but the check should not expect the same number of documents when a moveCollection runs in parallel.