Anomaly Detection not detecting host machines (learned OS)

Question

I have an ASA5540X firewall with the internal (software based) IPS module. The module has the up-to-date signatures and seems to be running correctly. However, after enabling anomaly detection (ad0), and specifying the internal zones, I don't see any "Learned OS" in IME
My settings are pretty basic for the sensor
access-list ips_traffic extended permit ip any any
access-list ips_traffic extended permit udp any any
class-map ips_class
 match access-list ips_traffic
policy-map global_policy
 class ips_class
 ips inline fail-open
not sure why it isn't learning the OSs

Answer 1

Learned OS maps—OS maps observed by the sensor through the fingerprinting of TCP packets with the SYN control bit set. Learned OS maps are local to the virtual sensor that sees the traffic.
can you verify the OS finger printing from
sensor# show os-identification learned
Enable passive-traffic-analysis {enabled | disabled}