I've previously run into a similar problem when trying to print high-resolution artwork for circuit-board manufacturing: the prints were on transparencies to allow for UV-photo-resist exposure and so had to be accurate, with no stray pixels. All artwork was done in a vector software.
The conclusion was that it depended on a number of factors. Updating the printer drivers (especially using the ones downloaded from the printer manufacturer, rather than the the plug-and-play ones) was a big part of it, though I expect given the sort of printer you’re using, this would have already been done.
Otherwise it seemed to be software dependent: printing within the vector program (directly from Adobe, Inkscape, Gimp, etc.) did cause artefacts to different degrees. Exporting to PDF and printing from there was better but often had other issues (the vector output in the PDF would appear as horizontal ‘blocks’ or ‘bands’ about 5 mm wide, which would separate when printing). Doing the artwork directly as a PDF, using LaTeX + TiKZ gave good results. We used multiple laser and inkjet printers and found varying results. Even a $10k Epson designed for high-resolution art printing had issues: we often found random stray dots (particularly on the laser printers) which seemed to be simply stray toner (this was at a single physical print dot size; important to us at that scale, but perhaps not important on the macro scale).
Ultimately we never found a complete solution: the issue seemed to be a mix of the way the software generated the data sent to the printer, and the way the printer converted that data into the physical print operation.
Beyond checking the drivers, the best you can do is probably to try different formats: ask the people who own/run the printer specifically what format they prefer. Try sending them a 300 DPI PDF for starters and see if it makes the problem go away or changes something elsewhere.