F5 load-balancers utilize a feature called "floating-ip". This is used by the F5 appliances in failover scenarios.
This article will describe how to enable MON on an F5 VM's "floating-ip".
When enabling MON on F5 LB vm you may see the VM status as "waiting for IP" in HCX UI under "network extension"
HCX
F5 Load Balancer
HCX relies on VMware tools to pull the IP address from the VM you are attempting to enable MON on. VMware tools can only see IPs attached to a VM network interface.
In the case of these F5 VMs this "floating-ip" is not attached to a VM interface therefore HCX cannot discover the IP.
Below workaround can be performed to enable MON: