Time stretching glitch in Garageband

I'm running Garageband 10.3.2 on OS High Sierra, and have been using the time stretching function to good effect before. However, on a latest project I've been working on, it appears that the function has decided to no longer work. Whenever I grab some audio and attempt to time stretch it, what happens is that the audio wave simply BREAKS at the point where I grab it and move it so that there's now a GAP (a break, as it were) where there should instead be a stretched (or compressed) audio track.

Is there any way to fix this?

Thanks in advance.