It appears someone already posted this, but there are no details and no responses. 104 people are watching the question though.
https://experienceleaguecommunities.adobe.com/t5/custom/page/page-id/GlobalSearch#q=Operating%20syst...
We're observing intermittent issues in February 2025 where OS and Mobile_ID are 0 in the hit data. It seems to coincide with our governance team reporting anomalies in the lookup files that come from Device Atlas, but I haven't been able to prove that as the root cause.