The soft lock is a bug! One pressure plate deactivates more than switch. It is still possible to beat the game, but only if you rescue Getrude before Jeremiah and Isabelle.
I've already fixed the bug, but I can't upload the fix before the rating period closes. So maybe come back next Tuesday or so. :)
The Hymn is a lock and key device that is usable in 2 places right now.
Thanks for playing, and so glad you enjoyed.