@lujop, mixed-content scenarios occur when there is a mix of HTTP and HTTPS links in the same bid response from advertisers.
We expect the traffic drop-off to be minimal (less than 5% during the time we queried results) and eventually zero as we move towards disabling non-secure bids in the near future. Hope that helps!
UPDATE
As of this time, setting sUseHttps to true will not cause mixed-content scenarios to occur. sUseHttps is used for ad requests as opposed to the WebView’s base URL for rendering creatives.