Are you able to change it so that it does not start at boot time (or login time) and instead is started manually? Or, can you cancel the password entry and just start it a second time by starting it manually? Does that make any difference?
Maybe someone in this topic: Signal App not usable - Flare preferred has more experience with Flare.
Does any other keyring password entry work? For example, when I start Geary, the system will prompt to open a keyring for Geary to get email passwords from. Do you use Geary? Does it have the same problem?