Warning icon on the device indicates that an action is assigned but cannot be used
Each action that has been assigned to the profile reserves that specific button or dial position. An assigned action always has a link between the mapped position ("the button") and the "action on the action panel".
In some cases the action on the action panel goes "missing"; The target application no longer has that functionality, the functionality has been significantly changed/upgraded, or it has been deleted for some reason.
For instance, some plugin updates might cause this issue if the previous actions have been replaced by new versions of the actions. 
When this happens, the Loupedeck system indicates that the action mapped to this position is not available and shows the warning icon as a message to the user.
This action can be removed normally or just replaced by dragging another action over it.
Note: Usually this happens with "Activate Aplication" actions. If user uninstalls the application from the computer, the action for launching it still remains mapped on the profile.