I have a simple workflow model, where few "Create Project Task" steps are there. In between the steps if I add "Lock Payload Process" (OOTB) and next step is a "Create Project Task" step, then in that step completion dialog, previous task comment is pre-populated.
I have never seen this. Lets see if other community members have encountered this.
You should do a short video and post that so ppl can see exactly what you mean