They attempted ever more forcefully to make users to set a PIN to protect server-side state; it started with a dialog at the bottom of the screen, obscuring about 20% of the user list, which could not be dimissed, and then after a few weeks progressed to the a full page dialog, which could not be dismissed - rendering the app unusable.
All you saw upon starting was the full page dialog demanding you set a PIN to continue using Signal.
I did not want any server-side state, and so did not set a PIN, and stopped using Signal. After a few weeks, the full-page dialog went away, and I found I could use Signal again.
Signal actually blocked usage of the app to force users to adopt unwanted new functionality. It's hard to imagine any app doing well with such mis-management.
I opened a thread discussing the problem on their support/public discussion forum, which was deleted. I also at first opened a bug report on Git, before I understood it was all intentional, this was also deleted.
Since this experience, I've regarded Signal as on the way out, but it's still the best there is right now.