MaxConcurrentCount is not working

[mvn-bachhuynh-dn]

Hi there! I try to set MaxConcurrentCount but it seems does not work.

Here is my command

aws cloudformation update-stack-instances \
    --stack-set-name Dev-SwitchRoleTerraform \
    --accounts '["19613xxxxx","25913145xxxxx","5116737xxxxx","62613390xxxxx","70865695xxxxx"]' \
    --regions '["ap-northeast-1"]' \
    --operation-preferences FailureToleranceCount=10,RegionConcurrencyType="PARALLEL",MaxConcurrentCount=10
{
    "OperationId": "d0b51a79-ab5a-46cc-b717xxxxx"
}

After that I tried to update-stack-set, modify some parameter, but It only run one by one!

Please help me!

Thank you!