Issue with lookupdisplay after migrated the code to PB12.6

Hi Team,

We are migrating our applications from PB12.5 to PB 12.6, as part of migration we are facing some issue with lookupdisplay() in datawindow expression. We have tried with the PB 12.6 build 4088. Application crashed wherever the lookupdisplay expression is used. We have tried with using the datawindow expression directly in the code, after that crashing issue is fixed but, the datawindow with lookupdisplay expression is not loaded properly.

Can you please suggest some ideas to fix these issues.?

Thanks in advance.