Hi @TimBo4
segmentMembership is the attribute that is updated after the segment evaluation job runs. The membership is updated for each profile that falls within the segment defintion.
For example, segmentMembership for a specific profile updates when that profile is realized or exits a specific audience.
As for the numbers you are seeing for segmentMembership, that looks different than what i'm used to seeing. Can you potentially go into one of those profiles and give an example? Hiding any PII, of course.