I have a publisher action with a Predefined Field Value that is showing correctly in Classic but not in Lightning.

It's for a reference text field where the Predefined Field Value formula takes the current reference and adds 1 to it. Here's the formula:

"-" + TEXT(VALUE(RIGHT(MyObject__c.MyReferenceField__c, 1)) + 1)

If the current value is "-1," then I want the publisher action to display "-2." This works as intended in Classic, but in Lightning, it continues to show "-1."

Any thoughts?