Jellyfin groups episdoes as "specials" even when <season> tag is present in the NFO

[Родион Панарин]

Both files have correct <episode>, <season> (filled with 1) and <anidbid> tags, and neither have <airsbefore...> tags or anything like that - yet when I open the wrongly-special-ed episode's metadata in the UI, Jellyfin lists "series number" as 0. Setting it to 1 for the episode fixes the issue, but since some of my anime r quite long (think 100+ eps), doing so manually would be troublesome. The NFO file remains the same before and after the change. Both episodes r in the same folder titled "Season 1", and the season.nfo has <title> set to "Season 1"; but Jellyfin displays some of the episodes not just as "Season 1", but also as a "Specials".
Am I doing something wrongly?

the NFO file of the wrongly "special" episode:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<episodedetails>
  <plot />
  <lockdata>false</lockdata>
  <dateadded>2024-11-12 14:46:25</dateadded>
  <title>In the Eternal Night</title>
  <year>2011</year>
  <runtime>24</runtime>
  <anidbid>7160</anidbid>
  <art>
    <poster>...</poster>
  </art>
  <showtitle>Legend of the Galactic Heroes</showtitle>
  <episode>1</episode>
  <season>1</season>
  <aired>2011-11-14</aired>
  <fileinfo>
    <streamdetails>
      <subtitle>
        <codec>ass</codec>
        <micodec>ass</micodec>
        <width>0</width>
        <height>0</height>
        <language>rus</language>
        <scantype>progressive</scantype>
        <default>False</default>
        <forced>False</forced>
      </subtitle>
      <video>
        <codec>h264</codec>
        <micodec>h264</micodec>
        <bitrate>2136409</bitrate>
        <width>960</width>
        <height>720</height>
        <aspect>4:3</aspect>
        <aspectratio>4:3</aspectratio>
        <framerate>29.97003</framerate>
        <language>jpn</language>
        <scantype>progressive</scantype>
        <default>True</default>
        <forced>False</forced>
        <duration>24</duration>
        <durationinseconds>1445</durationinseconds>
      </video>
      <audio>
        <codec>aac</codec>
        <micodec>aac</micodec>
        <bitrate>192000</bitrate>
        <language>jpn</language>
        <scantype>progressive</scantype>
        <channels>2</channels>
        <samplingrate>48000</samplingrate>
        <default>True</default>
        <forced>False</forced>
      </audio>
      <subtitle>
        <codec>ass</codec>
        <micodec>ass</micodec>
        <width>0</width>
        <height>0</height>
        <language>eng</language>
        <scantype>progressive</scantype>
        <default>True</default>
        <forced>False</forced>
      </subtitle>
    </streamdetails>
  </fileinfo>
</episodedetails>


the NFO of the one that is recognized correctly:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<episodedetails>
  <plot />
  <lockdata>false</lockdata>
  <dateadded>2024-11-12 14:46:26</dateadded>
  <title>Hoch Kaiserin!</title>
  <year>2011</year>
  <runtime>27</runtime>
  <anidbid>12120</anidbid>
  <art>
    <poster>...</poster>
  </art>
  <showtitle>Legend of the Galactic Heroes</showtitle>
  <episode>100</episode>
  <season>1</season>
  <aired>2011-11-14</aired>
  <fileinfo>
    <streamdetails>
      <subtitle>
        <codec>ass</codec>
        <micodec>ass</micodec>
        <width>0</width>
        <height>0</height>
        <language>rus</language>
        <scantype>progressive</scantype>
        <default>False</default>
        <forced>False</forced>
      </subtitle>
      <video>
        <codec>h264</codec>
        <micodec>h264</micodec>
        <bitrate>2655840</bitrate>
        <width>960</width>
        <height>720</height>
        <aspect>4:3</aspect>
        <aspectratio>4:3</aspectratio>
        <framerate>500</framerate>
        <language>jpn</language>
        <scantype>progressive</scantype>
        <default>True</default>
        <forced>False</forced>
        <duration>26</duration>
        <durationinseconds>1595</durationinseconds>
      </video>
      <audio>
        <codec>aac</codec>
        <micodec>aac</micodec>
        <bitrate>192000</bitrate>
        <language>jpn</language>
        <scantype>progressive</scantype>
        <channels>2</channels>
        <samplingrate>48000</samplingrate>
        <default>True</default>
        <forced>False</forced>
      </audio>
      <subtitle>
        <codec>ass</codec>
        <micodec>ass</micodec>
        <width>0</width>
        <height>0</height>
        <language>eng</language>
        <scantype>progressive</scantype>
        <default>True</default>
        <forced>False</forced>
      </subtitle>
    </streamdetails>
  </fileinfo>
</episodedetails>