Handbell soundfont issues

(I posted this in General Discussion yesterday because I didn't realize there was a Soundfont section, oops!).

I've been wanting to make a handbell soundfont for a long time now, and I finally have access to the necessary equipment to do so. I recorded some samples yesterday, but now I'm running into some issues with Polyphone.

When I play back the audio under the Samples tab it sounds great, but when I play it back under the Instruments tab it sounds awful, despite not doing anything to the audio itself.

This video hopefully illustrates what I'm talking about: https://youtu.be/DcrRPKeCsJY
Why does it sound so awful under the Instruments tab and how can I fix it?