It may very well be your paper.
To cut a long story short, your print engine is expecting the paper to arrive at and clear certain optical sensors at very precise times. If the paper slips by even a very small amount, it can result in a paper jam or other event being triggered.
If there are say 4 feed rollers across the paper input path, the A4 sheet will be pulled by all 4. If you put in narrow mug paper, it may only have two pulling it in and one of those rollers may be slightly worn thus slipping. Any subsequent sets of internal rollers may be worn too causing the same issue.
If the paper is not within tolerance then it can also cause a jam event to trigger. If the paper is too short or too long then it may be causing an optical sensor to trigger a jam as the paper either hasn't cleared when expected or has cleared a sensor too early.
Hope that makes sense
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