HALion is constantly monitoring the width of all busses in the signal path and adapts to the required width automatically.
For example, changing the bus width is required when you add a surround sample zone to a layer that only contains stereo samples. In this case, the layer bus and all following busses are set to surround, to allow for a correct routing. Stereo samples are still routed properly to channels 1 and 2.
Another way to change the bus width in the middle of the signal path is to add a surround panner to one of the insert effect slots of a stereo bus. In this case, the output of the bus changes from stereo to surround and forces all following busses to do the same.
AUX busses change their bus width, too, if they receive signals from surround sources.
Output busses cannot change their bus width automatically, because they are usually connected to a hardware device. Therefore, the routing to the plug-in output busses has to be changed manually. Make sure that surround slots are routed to the surround output and that stereo busses are routed to one of the stereo outputs.
If your routing is not set up correctly, the affected channels show a red warning icon to indicate that two or more busses are of the wrong width and that you risk losing signals from audio channels that cannot be processed.
In this case, you can connect surround busses to stereo outputs, for example, or add the Downmix effect to one of the inserts, thereby reducing the bus width to stereo, for example.