Ok, I have tried various things to get this to work. I was able to reproduce what you were seeing, with it working on a single incident but not multiple. Unfortunately that may be a bug. I noticed in the war room of each respective incident, there is an entry saying the close notes were modified, but it isn't actually modified. You are welcome to report it via support.paloaltonetworks.com
As far as other options, I also tried this in a post-processing script, but fields are kind of locked into a limbo state during post-processing and can't really be changed. If you attempt to set them, they just return to what they were prior to being set.
I unfortunately am not able to come up with any way to get this working as far as your current flow goes.
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