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What you describe could be a consequence of a hardware failure - probably a paper position/presence sensor - or, it could be a consequence of a wrong setting in the printer's driver settings or Properties (on Windows PCs).
The first setting to check on in this case, is the automatic size sensing function, which if you disable it, may correct the problem.
Also check whether you have chosen the exact right settings size. While an ill-detected settings size might be caused by a slightly defective paper position sensor, it could also be caused by a slightly inexact size being entered e.g. in a Custom or User Defined paper size.