There is some variance between devices but basically fingerprint data storage / handling at least ought to be dictated by Android rules for biometric data - which is roughly: data acquired from biometric sensors is never available in raw/usable form. Access to sensors, data acquisition, processing, and matching is done in hardware backed trusted execution environment. When/if data is stored outside tee, it is encrypted in a way that makes it accessible only by tee sw on the device where it was originally recorded.
Data is signed with a device specific key and thus by design is not transferable from one device to another.
There probably is fingerprint data in the backup (under /var/lib/sailfish-fpd/) and - since it is invalid due to originating from another device - it is confusing some parts of the sw stack. You probably need to get rid of it. Something like:
- systemctl stop systemctl stop sailfish-fpd
- /usr/libexec/sailfish-fpd/fpslave --remove-all
- /usr/libexec/sailfish-fpd/fpslave --flush-cache
- systemctl stop systemctl start sailfish-fpd
No and no.