To me it most likely might be the data transfer from premiere / the nle to voukoder pro. That means slight losses can happen, because the video gets always decompressed, send to voukoder pro and then recompressed. but this is the way each nle works. there is no way around it.
That does seem to be the case. after more testing, the only way i was able to get identical results was by inserting the footage as an image sequence with specifically rgb24 as its pixel format, and then exporting the footage as an image sequence again. other than that, whether i use voukoder or just premiere, the export is a bit lossy. definitely an issue on premiere's side, thanks!