Launch-powered GA property reporting fewer pageviews than GTM-powered GA property

[#1]

Hello, 

I'm trying to migrate my GA setup from GTM to Launch. To ensure a smooth migration, I decided to set GA via Launch on a test GA property first.

So I have both Launch and GTM set up on my website. Each of them is currently running a GA setup. The setups are functionally identical but reporting data to two different GA properties.

I noticed that the Launch-powered GA property is consistently reporting fewer pageviews than the GTM-powered GA property. Even if I narrow down the comparison to one single page, and compare day by day, via Launch I get on average 1.5% fewer pageviews than via GTM.

I know that these figures cannot perfectly coincide because network requests sometimes fail.

However, it seems to me that the 1.5% gap is a bit too big.

What is even more alarming is that it's always Launch reporting smaller figures. So the reason seems to be in Launch, and not in some random network issues.   

Do you have any idea as to why this may be happening and how to fix the Launch setup?

Thanks. 

PS. To implement GA in Launch I use the extension Google Global Site Tag (gtag) by Acronym. Both of my GA properties are GA360 properties (so it's not a sampling issue).

[#2]

There are several reason why Launch could be reporting numbers:

1. Can you narrow it by browser type? This could be related to a specific browser
2. It could also be ad blockers allowing Google to fire but not Launch to fire. If possible, check to see if your numbers correspond to the same in Adobe Analytics. 

If you have the client ID available as a custom dimension, try to cross-reference it between the two properties and see if you can narrow down the type of user who is missing your Launch GA impementation.

[#3]

I have done similar data collection before, it will be different, but mine is more deployed through Adobe Launch, the error is not large, I think it is acceptable.