Ive noticed this too.
Since around 18th October not a single sale has a conversion summary.
I have reported it to support and they have come back and told me its because:
- The customer was using a private browser (to prevent tracking) or an app that prevents the tracking of browser cookies.
- The customer has cleared their cache and cookies, which will erase all previous browser data used for tracking.
- They switched devices to prevent accurate cookie tracking.
I dont think this is right though, you dont go from pretty much every order shows conversion details to none at all.
I have asked Shopify Support to look into it more so waiting to hear