Hi Paul,
Question 1: Thanks for the clarification. I was already thinking if that might be an issue due to the typical signal dropout in T2 fMRI scanning.
Question 2: You wrote that "In your case, this looks like a "false positive" at the edge of the mask". This is good to know because in the three subjects where this problem occured, it always showed up at the very side of the brain (and not somewhere in the brain) and without showing bright lines between the red dashes.
Thanks again for the support and I wish some good or relaxing christmas days soon.