Secure backup failed and can't be restarted manually

Guidelines

• I have searched open and closed issues for duplicates
• I am submitting a bug report for existing functionality that does not work as intended
• This isn't a feature request or a discussion topic

Bug description

I noticed an error message telling me that the last automated online backup had failed and that I should manually retry. The progress bar was stuck at some medium percentage. I pressed the X button and afterwards the "backup now" button (or whatever it's called in the English version). The button does nothing. No error, just nothing.

Phone is connected to WiFi which is working perfectly. I even tried turning on backups over mobile data to ensure it wasn't some strange WiFi issue, but no change. Debug log attached below.

Screenshots

Circled button does nothing at all when pressed

Device

Fairphone 4

Android version

15

Signal version

8.21.5

Link to debug log

https://debuglogs.org/android/8.21.5/7533771f131d1c4da4391ac5be0f37ebe177e29bff0ae1e125470c64916669c6

Start with the attached debug log and reproduce the failed automated backup on the backup screen using the reported Fairphone 4, Android 15, and Signal 8.21.5 setup. Trace what happens after dismissing the stuck progress bar, then verify that pressing the manual backup button starts a new backup and provides visible progress or an error.