Google this month created a page with the limits of Google Ad Manager, and it stated that the limits will apply from May 1st. The introduced limits remove control from publishers, as they will not be able to customize the auction as they want. The tweak in the line item setup is described here. Some publishers were setting up House line items using AdSense or Ad Exchange creatives.
According to Google rules, unless otherwise authorized by Google via a contract amendment, publishers can only use line items for the specific purposes described, otherwise, Google will treat the Line Items as invalid activity.
Sponsorship and Standard line items may only be used for representing guaranteed demand. For example, to represent a direct advertiser deal with a fixed price and guaranteed volume, Google clarified. The Price Priority, Bulk, and Network Line Items only be used for representing non-guaranteed demand. For example, use these to represent third-party ad networks or exchanges. The House line items may only be used for representing demand where a publisher, the Ad Manager account holder, own the product or service being advertised.
Google also stated that Google Ad Manager System Limits and Line Item restrictions do not have to impact private marketplace deals booked as Sponsorship or Standard line items, and that over 99% of the partners are using line items correctly, and don’t need to change anything. For partners impacted, most are incorrectly setting up AdSense or Ad Exchange line items.