The problem is that the subtitles come out incorrectly, saying it's not the right time.

[Potmarigold]

bug.txt

When the source is entered in smi subtitles, the subtitles are displayed incorrectly and overlap with subtitles from other times.
This bug persists from the start of the video until the time of the subtitles.

[Masaiki]

I would say that subtitle formats other than ass srt sup are currently in a state of non-maintenance.
It may be a bug but I don't have the energy to fix it.
As an alternative, you could try converting them to the equivalent ass format subtitles