I have done some debugging on this. I inserted 

                  printf("output plugin activated for clipboard: %s\n", (*out)->get_id());    

at line 1202 of src/ui/clipboard.cpp.

The routine ClipboardManagerImpl::_onGet is called repeatedly (presumably triggered by an external program creating a clipboard read request), with different possible clipboard formats.
In my case, I was running Matlab and Teamviewer, and the following clipboard requests were tracked over a 10 second period:

output plugin activated for clipboard: org.inkscape.output.svg.inkscape
output plugin activated for clipboard: org.inkscape.output.png.cairo
output plugin activated for clipboard: org.inkscape.output.svg.inkscape
output plugin activated for clipboard: org.inkscape.output.svg.inkscape
output plugin activated for clipboard: org.ekips.output.dxf_outlines
output plugin activated for clipboard: org.inkscape.output.sif
output plugin activated for clipboard: org.inkscape.output.svg.inkscape
output plugin activated for clipboard: org.inkscape.output.wmf
output plugin activated for clipboard: org.inkscape.output.emf
output plugin activated for clipboard: org.inkscape.print.eps.cairo
output plugin activated for clipboard: org.inkscape.print.ps.cairo
output plugin activated for clipboard: org.inkscape.output.png.cairo
output plugin activated for clipboard: org.inkscape.output.svg.inkscape
output plugin activated for clipboard: org.inkscape.output.svg.plain
output plugin activated for clipboard: org.inkscape.output.svgz.inkscape
output plugin activated for clipboard: org.inkscape.output.svgz.plain
output plugin activated for clipboard: org.inkscape.output.LAYERS
output plugin activated for clipboard: org.inkscape.output.ZIP
output plugin activated for clipboard: org.inkscape.output.latex
output plugin activated for clipboard: org.inkscape.output.jfx
output plugin activated for clipboard: org.inkscape.output.pov
output plugin activated for clipboard: org.inkscape.output.pdf.cairorenderer
output plugin activated for clipboard: org.inkscape.output.svg.inkscape
output plugin activated for clipboard: org.ekips.output.dxf_outlines
output plugin activated for clipboard: org.inkscape.output.sif
output plugin activated for clipboard: org.inkscape.output.wmf
output plugin activated for clipboard: org.inkscape.output.emf
output plugin activated for clipboard: org.inkscape.print.eps.cairo
output plugin activated for clipboard: org.inkscape.print.ps.cairo
output plugin activated for clipboard: org.inkscape.output.png.cairo
output plugin activated for clipboard: org.inkscape.output.svg.inkscape
output plugin activated for clipboard: org.inkscape.output.svg.plain
output plugin activated for clipboard: org.inkscape.output.svgz.inkscape
output plugin activated for clipboard: org.inkscape.output.svgz.plain
output plugin activated for clipboard: org.inkscape.output.LAYERS
output plugin activated for clipboard: org.inkscape.output.ZIP
output plugin activated for clipboard: org.inkscape.output.latex
output plugin activated for clipboard: org.inkscape.output.jfx
output plugin activated for clipboard: org.inkscape.output.pov
output plugin activated for clipboard: org.inkscape.output.svg.inkscape
output plugin activated for clipboard: org.inkscape.output.svg.inkscape
output plugin activated for clipboard: org.inkscape.output.pdf.cairorenderer


As can be seen, the repeated requests cause Inkscape to try and export the copied data every few seconds, in multiple formats. 
Some of the formats cause errors, for example 

   org.ekips.output.hpgl
   org.inkscape.output.plt

So one temporary workaround to prevent the error dialogs is to remove those extensions:

    cd /usr/local/share/inkscape/extensions
    files="
      gimp_xcf.inx
      dxf_output.inx
      hpgl_output.inx
      jessyInk_export.inx
      plt_output.inx
      sk1_output.inx
      svg2fxg.inx
      svg2xaml.inx
      ink2canvas.inx
    "
    for x in $files ; do  sudo mv $x $x.disabled ; done

(you may need to do this in /usr/share/inkscape/extensions, depending on installation).


However this doesn't fix the underlying problem, and inkscape is still silently exporting the clipoard many times a second in many other formats.