Troubleshooting 'Not Set' System Attributes in MP Implementation

Hi! I have an MP implementation on a product thats 1 Website + 2 apps. We are seeing a Decent number of Not Set for system attributes like OS, Device etc. All OSs are showing when we do an OS level breakdown. Can anyone help identify what could be causing this? Eg here is a screenshot of conversion rate by OS. We can see that the highest conversion rate is from a not set device: Eg Also another report by device type also shows not set as the highest conversion rate