I haven't used Signal desktop, but I find Electron apps in general to be very wasteful of system resources. Out of curiosity, I once compared an Electron-based chat app to a C++ alternative, and found that the former used about 25 times the RAM and generated more CPU load.

If GP's system resources are usually dedicated to other tasks, perhaps trying to run an Electron app on top of those led to resource contention, and poor performance. You wouldn't notice this if your hardware is overprovisioned for the things you do with it.