Please enter a valid last name

With: Billing Last Name -> Mandatory -> Yes

Users who have edited their profile and added a First and Last Name are halted at checkout with the error: Please enter a valid last name.

I tested and indeed entering the correct last name produces the error.
I also found that deleting the Profile Last Name continues to produce the error.

With: Billing Last Name -> Mandatory -> No
Obviously the error is not produced and the checkout proceeds.

Further, users who never edit their Profile by adding First or Last Name do not encounter the error.

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