Can you please provide a link to the module in question?

Note: If a sampled note dies "naturally" (i.e. there is no explicit note-off event and the sample just reaches its end), then there is no way for the MIDI export to know that. It will just keep playing the note until there is a note-off or another note. on the same channel (assuming NNA is not set to "continue"). Given that note-off works in general, maybe this is what is happening here.

Should be this one: https://modland.ziphoid.com/pub/modules/Impulsetracker/Skyline/8-bit%20kids%20with%20dreams.it

So yeah, the chord instrument has NNA=Continue. It might be possible to send a note-off once the volume envelope reaches its end, but apart from that, in general case, there is little that can be done here.

As a workaround, set the New Note Action of instrument to anything but "Continue" for MIDI export. You cannot expect MIDI conversions of just about any module to sound correct because there are just too many differences between module land and MIDI land, and this is one of them.

I had a closer look at the export code again and decided that trying to "fix" this would make the export more complex than it should be. As mentioned above, there is a reason why this happens, and there is a workaround that you can use for exporting this module without troubles. Hence I'm going to close this issue.