It appears that when using Asterisk with an SBC, we do not receive any lagged or unreachable messages.
However, devices connected direct to Asterisk (in both cases from external networks) show both lagged and unreachable.
Further to this, we find that many devices are showing in Asterisk as Unknown, yet the SBC has them active/registered.
Is it the fact that the all traffic from the SBC comes from one IP and Asterisk is getting confused?
Is is that you can not use qualify with an SBC (I could not find anything stating not to)?
There is not enough information or detail to answer your question or explain what is going on. You would need to provide configuration information, console output (with SIP logging on), and a description of the setup. Qualify itself doesn’t care about whether something is an SBC or anything else - it sends a SIP OPTIONS request out and if it gets a response then it is happy.