We have set up conditional two-factor authentication for the majority of our user profiles. It appears that some of these login flows broke recently and we seeing the following error:

Error
caused by element : FlowApexPluginCall.Validation
caused by: Too many token validations for user

Please could you clarify what can cause "too many token validations".
What has been the likely cause of this issue? What steps can we take to ensure this does not happen again and block our users from salesforce? 

 

[400] Bulk API HTTP Error result: <?xml version="1.0" encoding="UTF-8"?><error
   xmlns="http://www.force.com/2009/06/asyncapi/dataload">
 <exceptionCode>InvalidUrl</exceptionCode>
 <exceptionMessage>Destination URL not reset. The URL returned from login must be set</exceptionMessage>
</error>

This still works for eu2.salesforce.com for example but is not working for the soon to be migrated to login.salesforce.com.

Will this work on the go live of the new login sub domain?

[400] Bulk API HTTP Error result: <?xml version="1.0" encoding="UTF-8"?><error
   xmlns="http://www.force.com/2009/06/asyncapi/dataload">
 <exceptionCode>InvalidUrl</exceptionCode>
 <exceptionMessage>Destination URL not reset. The URL returned from login must be set</exceptionMessage>
</error>

This still works for eu2.salesforce.com for example but is not working for the soon to be migrated to login.salesforce.com.

Will this work on the go live of the new login sub domain?