Name of a variable set should not be empty
The mandatory fields had been changed on the creation of variable set since London.
The message is coming from the OOB business rule "Validate Name". This business rule is active in Kingston but during the upgrade, it needs to be turned into 'inactive'. But somehow it skipped that action(set to false).
Setting the business rule "Validate Name" on the table 'Variable Set [item_option_new_set]' will resolve this issue.