Hi @filip_g,
From experience, it’s likely to be one of two things - bad rows or tracking configuration.
I’d start with bad rows - where data doesn’t conform to the schema, it’ll land in the bad bucket rather than going through to the database. Here’s a post that should help with checking this. If there’s something being sent as the wrong type - like an SKU sent as an integer, then this will happen.
If it’s not bad rows you should take a closer look at how the tracking is configured. The fact that some but not all the data is present is interesting - when the script fires is relevant insofar as it’s possible for the user to navigate away from the page before it does so. If you’re using a tag manager then I’d look into the triggers, and if it’s code directly on page I’d pay close attention to where on the page the script is fired.
I hope that helps. Let us know how you get on.