It could be you have a document large enough that the printer cannot render it in one go, therefore it's rendering part of the job, printing it then rendering the rest.
The printer has several stages, warmup, initial rotation, print and final rotation etc, if the formatter has not told the print engine to enter final rotation then standby the engine will continue to rotate, I don't believe this is a hardware fault, more likely the file is causing the printer to try and work around it by printing part of it and then rendering the rest.
A simple test would be to print 25 pages of plain text to see if that prints (and the on board paper path test as suggested).
I've seen this issue in the field and in some cases cured it by dropping the graphics quality in the print driver to 300dpi, this reduces memory needed by 75% and if the same document prints fine the issue is file size / memory.
