I sent Piper to Spectacle Island a while ago to play with new companions, and until recently she just wandered around like everyone else there. After the latest patch however, I can't find her anywhere. I know she's still supposed to be on Spectacle Island as I heard her dialogue just a little while ago (along with the subtitles). Anybody else have this issue? I'm on PS4 by the way.

I'd suggest fast traveling back and forth to the location you said you heard her (maybe sleep or wait while away from that location). It sounds like she may be stuck somewhere you can't see and she might respawn if you travel back into the cell she is in. I've lost track of settlers like that and found them when I traveled back after a stint of adventuring.

If you had access to the console commands, this would be easy, btw.

Do you have a bell constructed there, she will come to the bell when you ring it.

Or if you have romanced her, just go sleep in a bed at spectacle, when you wake up she should crawl out of bed with you.