Are you getting PEGA0050 alert as well in Pega alerts log?
This exception is triggered when the system determines that a rule or activity copies a clipboard page list to another list in a way that is inefficient and, in the Pega 7 Platform, no longer necessary. So, maybe your "Append and Map To" is inefficiently working.
The following settings in the prconfig.xml file implement this alert:
<env name="alerts/virtuallists/copy> – This setting enables lightweight list Copy alerts. The default value is True. You can alter it to false as per your requirement, if it isn't present you can add it.