YouTube traffic went down 5% — how would you report this issue to your manager?

I have a few clarifying questions to better understand the problem statement. 

1.  when you mean by YouTube, can I assume that you are only referring to the primary YouTube application and not other properties such as YouTube Music or YouTube TV.  - Yes

2. What do you mean by traffic? Is it people visiting YouTube.com, people searching for YouTube videos or amount of time that people spend watching videos on YouTube?  - Good question. We see 5% drop across all of the above. 

Thanks!. I will expect YouTube DAU is typically in Billions. 

3. Is this a sudden drop or a gradual drop – Sudden

4. Hmm.. Are we seeing this drop in a particular geographical location - say North America, Europe, Asia etc.  - No, we are seeing this primarily in Western Countries (North America, US and Europe)

5. Interesting..  Are we seeing drop specific to any specific clients or device types (such as Browser from computers, Android, iPhone etc) –  No. we see it across all our devices.

6. Was there any major geo political event that happened prior to this drop? – No

Cool. this helps. This rules out that any external factors such as sudden geo political events contributed towards this sudden drop. 

Ok, let us now dig internally to see if our team might have rolled out a change that could have contributed towards this. 

1. Was there a code change that was rolled out prior to this sudden drop? – Well, YouTube engineering team rolls out code changes multiple times in a day. So, yes. 

Sure. I bet YouTube is continuously doing a lot of experiments to better learn about our users. Sometmes, we do experiments specific to a geo graphical location or customer segment. Because, we now know that this impact all users across multiple geographical locations, I will be only interested to find out the code changes that was widely rolled out in the recent weeks. So, what changes were widely rolled out in the recent weeks especially before we noticed a drop ? – Yeah, we rolled out changes related to how YouTube site respond to non English language users.

Thanks. I believe this change has to be contributing towards the 5% drop. 

To summarize, I will report to my manager that we observed 5% drop in YouTube acquisition, activation and engagement metrics because of our internal code change targeted towards non-English language users. I will then recommend to my engineering team to rollback this change.