Using focal OTA1, fingerprint is working on my Mi A2 with a Goodix fingerprint sensor. It also worked flawlessly with different versions of xenial UT.

If I recall correctly from lineageOS forums in XDA, Mi A2 can include two different fingerprint sensors: Goodix and FPC. This may be related to some devices having problems with fingerprint under UT. To check the type of sensor, in my phone there is a folder /sys/class/goodix_fp.