Your desktop flow failed to run with the error code NoCandidateMachine or the error details "No machine able to run the desktop flow has been found".
When there are no available machines, Power Automate will create a queue that holds the desktop flows waiting to be run. Once a machine is available, the next desktop flow run will be selected based on priority and time of request. If no machine is available after three hours since the time it was requested, the desktop flow will time out and fail with a NoCandidateMachine error.
There can be several reasons why your desktop flow times out with a NoCandidateMachine error:
The machine is offline. Start up your machine, then make sure that Power Automate Desktop is properly installed and the on-premise gateway is active.
The machine is busy. If your desktop flow times out after the three hour time period, it is likely that the allocated machine resources are not sufficiently scaling to meet the workflow demand. Adding more machines would help distribute the workload.
The machine is no longer usable. Add a new machine, then update the desktop flow connections in your cloud flows to use the new machine.
In the event you have a backup of desktop flows in your run queue due to one of the above reasons, you can bulk cancel your desktop flow runs by canceling the parent cloud flow run using the Cancel parent flow run action on the Desktop flow runs page. Once your machine issue has been resolved, you can re-launch those cloud flows.