Scan time is the rate the OPC driver is polling the device.
Timeout is how long you have till it says it's bad.
Certain conditions can cause it to get a bad read from overloading the comms on the PLC side but I don't think you'll be able to cause that problem over a radio network. It's a thing that can happen but I don't think it's your problem.
I would recommend setting up a longer polling rate on your tag groups. You configure tag groups by clicking the drop down in the tag browser and selecting "Edit Tag Groups". This lets you make a custom tag group that polls slower. Then you can mass edit tags to assign them to the slow polling group.
