There are some printers that have multi-level power-saving and sleep modes. The HP Officejet Pro 8500 is one of these. There is a common problem with that model and others with multi-level sleep modes, whether under Windows or Linux. They just goes to sleep and won’t wake up. The URL below is only one of the questions I found on-line that relate to this problem.
Since there are only questions and no answers on the Internet, it looks like the solution is to simply turn the printer off and back on. I have also found that, on the HP Officejet Pro 8500 at least, I can press the red X key and then replug the USB cable to get the printer to print.
This solution implies that the problem is that when the printer goes into deep sleep, the USB bus actually decides that there is nothing attached. The OS thinks that the device has been removed and removes any OS configuration for the device. When you try to print, the device cannot be found on the bus and so no data gets sent to the printer which would presumably wake it up so it would print. Pressing the red X key wakes up the printer and replugging the USB cable apparently is still required to notify the OS that a device has been added to the USB bus.
I have determined that while the printer is in the first level of power saving mode, it still responds when a print job is sent to it. It is only after the printer enters the deepest level of sleep mode that this problem will manifest itself.
This actually sounds quite like a design deficiency in either the printer itself or the USB interface in the printer.