Why would certain metrics drop in half while others double? (iPad only)

Question

I'm a developer on a website. Normally I don't work with analytics much, but we rolled a recent update that's causing a strange traffic situation and I've been tasked to investigate these Google Analytics issues.

The situation is that unique visitors and visitor traffic dropped by almost exactly 50% (hard to tell for sure because of daily variation), pageviews remained constant, and average pages per session and average session duration doubled.

I am wondering if anyone has some ideas on what could theoretically cause this type of traffic shift. The update involves a 3rd-party, so I am not in control of all the code that was changed. Nothing we did personally involved analytics, but they might have changed something.

Additional notes:

1. This issue appears isolated to iPads only.
2. It is possible that this is a normalization - that iPads were previously broken, and this is actually a correction. The data I have is suggestive of that, but I don't have the kind of breakdown I need yet to determine that for sure - I only have iPad vs everything, so I can't compare to other tablet metrics specifically.
3. I have been able to isolate it as being directly related to our update.

Edit: I got additional tablet data and was able to determine that this was not a normalization like I first suspected. Previous to this change sessions averaged approximately 90 seconds for both iPad and non-iPad. After the change iPads jump up to approximately 200 seconds on average.

Interestingly enough, non-iPad tablets also show a jump, but not as extreme - they go from 90 seconds to approximately 140. My hypotheses there is that some non-iPad devices are having the same behavior, but not all. I have device-specific data but it's a lot to dig through, so I'll be working on that next.

Answer 1

It sounds like since pageviews are constant, that users had previously been counted as two sessions. It sounds like it had been splitting a user's session in two. Now you're aggregating that session into one.

It's possible if you have sub domains that going from one sub domain to another will count as a new session. If you are using different analytics codes for different aspects of your website this is also possible.