I'm sure there's a perfectly good reason behind that. But I must say, I already forgot two pins and there's now a pop up for the third one asking me to insert it every time I open the app, and I have absolutely no idea what this pin is either. Not entering it though doesn't seem to be preventing me from using the app though, so that's also weird. Meh, still not too much of a deal breaker to stop using Signal.
I have my pin in my password manager, but I can't tell Signal that. So it hassles me all the time. If I try and disable pin protection it gives me a scary warning about losing all my messages.
they are asking you for the pin to remind you of it. When you enetered it correctly they are using a spaced repetition algorithm [0] for the next date they show that prompt.
