Forum is provided by "Invision Community" (same as for Toyota owners club), they do all sorts of advertising which can be configured in the main admin centre (by admin) as also by the end user (by accepting the terms). It seems there was a recent update to the forum which affected the adds. Even when setting the adverts to OFF they still appear!!!
From my understanding something has triggered this, it could be simply a bug in the privacy policy based on the recent application version or potentially browser type and version.... which means it may not affect everyone.
If this is not a bug someone is overriding the settings allowing all Google Adverts, potentially breaking privacy policy at the same time.