This is for the most recent version on MacOS. For any MIDI file I import, both the in-app video and the rendered video output cut around 4-5 seconds before the end of the MIDI file.
Example below, the image shows that the app thinks this song is 3:22 but there are still notes left even when the slider is set all the way to the right.

Sorry - I accidentally caused this issue when adding the new MIDI Synth in Version 1.16.
Will be fixed in Version 1.18.
Thanks for your patience
No worries! Quick workaround for anyone else having this issue is to just extend the MIDI file by ~10 bars to get the remaining notes to play
Version 1.18 is now available for Windows and Android.
Windows update available as a direct download: www.visualmusicdesign.com/seemusic
Android update available from Google Play Store
The iOS and MacOS versions are waiting to be reviewed by Apple, and should be available on their respective App Stores later today or tomorrow.