Procedure

It could be due to one or more reasons. Check the following:

1. Check that the device is still responsive - Make sure the device is powered up, running, and correctly connected to the right network (and VLAN).
2. Check the IP setup - Some devices may only be discoverable if the PC and the device are on the same network and also within the same IP range.
3. Check the Q-SYS Designer version - Devices running older firmware versions (especially before v7.0) may not be detected by newer versions of Designer. It is recommended to use the same version of Designer as the version of firmware running on the Q-SYS Core. Older versions of Designer are available here.
4. Check your PC's firewall - Each version of Designer you have installed will have its own set of firewall rules. It is possible that the rules for the version you are using does not allow full access to the network and thus is blocking traffic. Try temporarily disabling the firewall on your PC. If devices are then discoverable in Designer, check the firewall settings for the specific version of Designer you are using to make sure that all traffic is allowed. (Be sure to re-enable your firewall.)
5. Create a Hard Link (Cores only) - Device detection typically uses multicast packets and sometimes these can be subject to filtering by network switches. For a Core, you can bypass the usual detection mechanism by using a Hard Link in Designer. Configure Hard Links in File -> Preferences using the Core's IP address. The Hard Link will then show up in the list with a small indicator. If that indicator is green, it means Designer can see and communicate with the Core. For more information about Hard Links, see the Remote Connectivity topic in Q-SYS Help.
6. Power cycle the device - If none of the above works, try power cycling the device.
7. Connect directly to the device - If you are unable to detect the device over the normal network, try connecting to it directly from your PC and then repeat the steps above.