A VM cannot communicate with an external resource that initiates the connection. Flow and firewall logging are enabled and other VMs in the subnet can communicate externally, but you see no denied log entries for this VM. What is the most likely cause of the missing log lines?

The most likely cause is that the traffic is not matching the expected ingress rule. If an external resource initiates a connection to a VM, it's considered ingress traffic. If this traffic is dropped before it even reaches a firewall rule (e.g., due to routing issues, network ACLs, or the VM not listening on the port), the firewall logs won't show a denial because the firewall itself wasn't the component that dropped the packet. The fact that other VMs in the subnet can communicate externally suggests the issue is specific to this VM's ingress path. Matching an expected ingress or egress rule would generate log entries if the rule was configured to log, and an egress rule wouldn't apply to an initiated inbound connection.