Hi @Bill ! Looks like I missed you follow-up question on a previous Community post - apologies on that! Allow me to follow-up here. 

You would only expect 0 users in this cohort if users can only fulfill one of the conditions across all time. But if you have users who maybe started off with experiment “string_a” and then no longer have “string_a”, then those users will be counted in this cohort.

For example, I’m looking at a Playlists array and looking for users who contain value 108 sometime during the time period and also not contain value 108 sometime during the time period: 

https://analytics.amplitude.com/demo/cohort/5gbwy67

If I look up one of the users who fulfill this condition, I see that this user did have events where 108 value appeared in the Playlists array and also had events where the 108 value was not part of the Playlists array: 

https://analytics.amplitude.com/demo/chart/new/6m6nxgh

Hope this helps! 

Thanks Belinda...Bill