SoundConverter doesn't name files with DiscNumber

I am using Ubuntu 18.10 and SoundConverter 3.0.0, which is installed through ubuntu repo.
I've set up custom file naming scheme, which is:
{Artist} - [{Date}] {Album}/{DiscNumber}{Track} - {Title}
And in 'preview' I've got the right name, such as 201 - {Title}.opus (as I am using opus as output).
Original files are properly tagged, and they have discnumber tag, and it's showing properly on Windows machine in foobar. But when converting, instead discnumber I get 0, so the filename is 001 - Songname.opus. This is not good.
Originals are stored on NAS shared through Samba, and I added them to converter via drag'n'drop.
This is output from metaflac --list command, only tag part:

METADATA block #3
  type: 4 (VORBIS_COMMENT)
  is last: false
  length: 470
  vendor string: CUETools FLACCL 2.1.6
  comments: 18
    comment[0]: ALBUM=Pirate's Choice
    comment[1]: ARTIST=Orchestra Baobab
    comment[2]: CDTOC=6+96+99F1+12249+1C020+237B8+2B329+340BD
    comment[3]: DATE=1989
    comment[4]: DISCNUMBER=1
    comment[5]: GENRE=World
    comment[6]: LABELNO=WCD063
    comment[7]: ORGANIZATION=World Circuit
    comment[8]: RELEASE DATE=2001-10-01
    comment[9]: RELEASECOUNTRY=GB
    comment[10]: TITLE=Coumba
    comment[11]: DISCTOTAL=2
    comment[12]: TRACKTOTAL=6
    comment[13]: TRACKNUMBER=2
    comment[14]: replaygain_album_gain=-2.10 dB
    comment[15]: replaygain_album_peak=1.000000
    comment[16]: replaygain_track_gain=-3.03 dB
    comment[17]: replaygain_track_peak=0.997528

What to do?