hostapd debug messages?

Just upgraded my client to 12.2. My hoastap (v0.7.3) is on an unchanged 12.1 server.

Now my client does not “see” my broadcast SSID in NetWork Manager.

If I run my hoastapd in debug mode:
hostapd -dd /etc/hostapd.conf

I see a steady stream of messages like this:

STA <client mac addrs> sent probe request for broadcast SSID
mbmt: :proberesp cb

(repeated forever)

My assumption is that the first line is the hostapd saying that “I have received a request to broadcast my SSID”
And the second line is, hoastapd saying “My response to this probe request is, CB”?

But what is “CB”?

Regards, Martin