Thank you all for replying, and sorry it took me so long to come back to this. Bavi_H, you asked about the device that doesn't work for me. I use these midi files in a video game that I wrote. When I play that game on a Samsung Galaxy S20 FE phone, I run into these problems where I can't hear certain sound effect files (and can't hear some notes of some music files). If you're really curious, and have an Android phone/tablet/device, and want to see if you can reproduce the problem, you can get the game in Google Play:
(There are also graphical bugs on newer devices. I started noticing a bunch of issues after upgrading my phone, but it's mostly still playable. The Attack.mid file plays whenever the player shoots, so it's pretty easy to test that one.)
Jason, you mentioned that the pitch could be too high. I'm pretty sure that the pitch is part of the problem. The sound effects that I can hear are all lower. For example, this file seems to work just fine:
I think it's pretty much the same as Attack.mid, but each note is a little lower.
I might try multiplying the tempo and note durations by 8 like Bavi_H said. I'd be a little surprised if that works, since my other files have the same tempo and short notes and seem fine (I didn't realize they were so short since I don't really know what I'm doing).
I'll also try different instruments. Geoff, you mentioned changing the instrument to something with an instant attack, i.e. no Attack at all. Do you know where I could find a list of instruments with no attack at all? I tried a quick search but couldn't find anything. (I wasn't even familiar with that term until now.)
Again, thank you all. This seems like a very cool forum. I'm glad I tried it!