iOS 10 "Starting WebFilter logging for process" + Proxy-Authorization header removed from request

Starting from iOS 10 I noticed such logs in my app

yyyy-MM-dd HH:mm:sss HelloWorld[XXX:XXXXXX] WF: === Starting WebFilter logging for process HelloWorld
yyyy-MM-dd HH:mm:sss HelloWorld[XXX:XXXXXX] WF: _userSettingsForUser mobile: {
    filterBlacklist =     (
    );
    filterWhitelist =     (
    );
    restrictWeb = 1;
    useContentFilter = 0;
    useContentFilterOverrides = 0;
    whitelistEnabled = 0;
}
yyyy-MM-dd HH:mm:sss HelloWorld[XXX:XXXXXX] WF: _WebFilterIsActive returning: NO

I have reviewed iOS 10 Release notes but there is no info about WebFilter feature

Also I noticed that for some sites Proxy-Authorization removed from request (I use programmatically configured proxy) and this issue started from iOS 10.

Anybody can throw a light on this?

Update 1

I found stable case when this happens

1. WebView request / for some site example.org over https
2. Received html contains http link to some resource (image for css) like http://example.org/icon.png
3. This lead to Header removal

If you want to remove the message on the XCode’s console then, please find the below steps.

Select Product => Scheme => Edit Scheme or use shortcut : CMD + <
Select the Run option from left side.
On Environment Variables section, add the variable OS_ACTIVITY_MODE = disable

Check the site with Chrome Developer Tools and you will most likely find a warning like Mixed Content: The page at '...' as loaded over HTTPS, but requested an insecure resource '...'. This content should also be served over HTTPS.

According to Apple the "Content Security Policy (CSP) support" in Safari 10 "has been enhanced by including version 2.0 of the standard." It seems that this includes iOS 10 as well.

Have a look here about the CSP levels: https://content-security-policy.com

I was facing the same problem, the reason at my case was,I had tried to open video of .webm extension in iframe.When I changed extension of video from .webm to .mov or .mp4 the issue was solved.

I had the same messages, linked to no reward videos being served from AdMob.
I installed the latest AdMob framework - still same error.
Double checked that I had all settings in relation to AdMob integration correctly and then just waited.
One day later, all videos were delivered as expected, so I assume it was a problem on Google end.