Autonumbering in CRM 9.0

I have updated Autonumbering format for account number field with Sequence 9.

AttributeMetadata retrievedAttributeMetadata = attributeResponse.AttributeMetadata;
retrievedAttributeMetadata.AutoNumberFormat = "{SEQNUM:9}";
UpdateAttributeRequest updateRequest = new UpdateAttributeRequest
{
Attribute = retrievedAttributeMetadata,
EntityName = "msdyn_customerasset"
};
crmServiceClientObj.Execute(updateRequest);

Later, I am trying to update the format, say "ACC{SEQNUM:9}";

It worked initially, when we tried a month back, but now, even though the Update Request is executing, new format is not reflected to the attribute metadata. It still showing the number sequence.

If this can be done, can anyone help how to do this?