I ran into this issue when distro hopping when I first got my framework, tracked it down to my fingerprint being remembered by the device, but not the OS. If you enrolled a finger, but cant do it again, it might be this. In this thread there is a script you can use to wipe the reader memory and try again. I hope it works for you, I had a hard time getting the reader to work in anything until the distro included supported for it.