Hi Dan, thank you for the suggestion. I tried this after changing my script to save to a file geodatabase (instead of the in_memory workspace) and the merge worked just fine. However, attempting to do this same operation in script did not work even when using a file geodatabase instead of the in_memory workspace.
From the merge tool documentation I can see that the input should be a list of data filepaths, which is exactly what I am using for the input. The following code snippet is essentially* what I am doing in the script
damarea = "C:\\temp.gdb
damarea_list = ['in_memory\\polygon_D0511', 'in_memory\\polygon_D0510', 'in_memory\\polygon_D0512', 'in_memory\\polygon_D3239', 'in_memory\\polygon_D0514', 'in_memory\\polygon_D0515', 'in_memory\\polygon_D0513', 'in_memory\\polygon_D0509']
arcpy.env.workspace = "in_memory"
arcpy.management.Merge(damarea_list, damarea)
*I am leaving out a for loop where I first develop the individual featureclasses and then append them to the final list that you see in damarea_list.
The field mapping parameter is optional and since all input featureclasses have the exact same fields, I do not think I need it for the merge tool to work?
P.S. I did see that when I export to python from model builder, the input featureclasses is not provided as a list, but as a string with filepaths separated by a semicolon (;). I tried this in the script and it also did not work. Any other ideas?? I am at a loss and appreciate any help I can get here.
Thank you