GAM ActiveView impression tracking not firing since v10

[jamiedruce]

This was initially spotted by our AdOps team seeing viewable impressions drop down by about 60% inside of GAM, tracing it back we found it correlated with an upgrade from v9 to v10 of prebid.

I have since been able to reproduce this with a very basic implementation of GAM and PBJS on page and a single demo ad. This only happens when Prebid wins the auction, but can be seen very easily through the network tab of dev console, searching for activeview?, where scrolling the unit into view shows the network request get dispatched, but with v10, no such request takes place.

Evidence wise, you can see v9.53.2 here: https://cipt.demo.contentignite.com/prebid-example-v9.html
And v10.9.0 here: https://cipt.demo.contentignite.com/prebid-example-v10.html

Here is a loom showing the situation: https://www.loom.com/share/114682e0137e47f58ff8aef7c73c0171?sid=f2e8d437-2651-49d3-97f2-8065b16e492f

We were previously rendering the creative using banner.js, so to rule that out as the cause, we tried updating to the latest code, and also tried directly using the renderAd method, but were still seeing the same outcome.

An thoughts on this would be much appreciated, and curiously im keen to know if anyone else has seen this too.

[dgirardi]

Thank you very much for this! We had a couple similar reports, but none with this level of detail. The issue is related to the yielding of the main thread; #13789 turns it off to address it, and your examples just allowed me to verify the fix - of course you're welcome to do the same.

[jamiedruce]

Ah! Thanks for getting back so quickly @dgirardi, and for looking into this, much appreciated. Will keep an eye on that MR for the time being