I've been testing my H264 conversion script, and come across a problem with the VDR 1.6 subtitles

VDR 1.6 (.vdr) recordings
The subtitle stream is reported by VLC as type "subtitle",  "codec: DVD subtitles (spu)"
ffmpeg reports  "Stream #0:2[0x20]: Subtitle: dvd_subtitle"
For reasons unknown, subtitles do not show on VLC (although you can select the subs track), Kodi, mplayer and ffplay
VDR 2.20 + VOMP 0.4.1 shows subtitles CORRECTLY, so they exist in the stream.

VDR 2.20 (.ts) recordings
ffmpeg reports  "Stream #0:3[0x131](eng): Subtitle: dvb_subtitle ([6][0][0][0] / 0x0006)"

Subtitles show on VLC, ffplay and VDR 2.20 + Kodi (using VNSI)
Subtitles do not show on VDR 2.20 + VOMP 0.4.1

ffmpeg reports no subtitle data when transcoding / copying the VDR 1.6 streams, even when forcing the codec to "dvb_subtitle"
Obviously if possible I would like to retain the subtitle data when transcoding around 8 years of recordings.

Could someone please confirm :

a) Is there an issue with VOMP on VDR 2.20 re: subtitles and old VDR 1.6 recordings ?
b) Is there a Linux or windows video player that shows subtitles in VDR 1.6 (.vdr) recordings ?
c) Is there a magic switch in FFMPEG or other tool to recognise / transcode / export the "DVD subtitles" ? Or another program ?

If all else fails, I assume it's possible to extract the data using functions in old VDR 1.6 code, but that might be a bit involved...

Thanks !