On Web client, if one field has multiple related link lines defined for it, Hover functionality will fail if query of the first link line return no record. But on windows client, Hover functionality will go through all the related link lines until get record returned or reach the last link line. This is what is also expected on Web client. And Hover functionality works like that on Web client before.
Hover pop-up code has been refactored in SM9.41 Web Client to only return a value if the link query also returns a value. Customer has been advised to change their code to handle this situation.