Missing logged in users in UserID reports

Hi, I have just set up Matomo in Wordpress specifically to monitor website use by members. I have set up the UserID reporting against emails and most users seem to be picked up. I can check this as I use Simple WP Membership and can see when they logged in. However some users are not picked up by Matomo in UserID reports.

I have checked their status and they are all Wordpress ‘subscribers’ so it is not clear why they might be treated differently and missed from Matomo UserID reports.

Any suggestions gratefully received.



Maybe they are using an adblocker that blocks Matomo.
Maybe they have set their browser to DoNotTrack which Matomo respects.
Maybe they have used the opt-out iFrame to opt out of the tracking.