Check if vulscan.exe is running on these clients - if it is, it will cause the scheduled task to wait as you have described until vulscan is finished. You can check from the console by right-clicking on the computer -> Inspect -> Processes tab and look for vulscan.exe under LANDesk processes (top section by default I think). If you see it, you can kill vulscan.exe by right clicking on the process. After a minute or two, the scheduled task should kick in for that device. Vulscan should just run again the next time it is scheduled, depending on your agent settings.
Thanks Dave, unfortunately on each device I've tried, the inspect option (although available), comes up saying it can't connect to device when trying to look at processes.. same for services.
Just puzzled why so many devices are suddenly having this issue, nothing about the agent or config has changed that I know of
Can you verify the agents are the same version as the core and if they have the Management Services running or even installed on the clients that have the issue.