Verification on a VBScript label expression is deemed valid when fields are added without an operator.
Last Published: January 18, 2017ArcGIS Pro
Bug ID Number
December 17, 2014
November 24, 2020
After review by the development team, it has been determined that this issue is related to a known limitation with the software that lies outside of Esri's control. The issue's Additional Information section may contain further explanation.
It’s a valid label expression that doesn’t really do anything, which is why it doesn’t label in Pro.
The expression declares two string variables in a row that don’t concatenate or anything. This will return null.