The issue was 1st reported here:
https://sourceforge.net/p/forge/site-support/11347/ <—I was unable to duplicate this one if I use my account "jwb1980" <—(SF Admin account) but I could duplicate it if I use a test account (username) I checked out the permissions and from what I can tell anyone that logged in should be able to see the post :https://sourceforge.net/p/phplot/admin/discussion/permissions
The issue/bug is that post/thread, is under https://sourceforge.net/p/phplot/discussion/46381/ and it supposed to prompt for login or gives a 403 unless your account is a member of the project:
go to https://sourceforge.net/p/phplot/admin/discussion/forums
"zzz (OLD) ..." discussion 46381 is set to "Only viewable by members"
The issue is that "Post by killerjo on write image to disk" should not show up unless I'm a member of the project.