The collmod coordinator uses checkAllowMigrationsOnConfigServer in two places to early exit if the coordinator has already completed work. The first is present since 7.0 while the second is introduced in master recently (9.1) and will be backported. However, in 9.0FCV+, checkAllowMigrationsOnConfigServer does not guarantee that resumeMigrations completed correctly since the config server is updated before the shards are.

This can lead both collmod early exit branches to exit with chunk operations still disabled on the shards. This will prevent all chunk operations (move, merge, split) on that collection.