https://wccftech.com/galaxy-s10-and-note-10-fingerprint-sensor-vulnerability-to-be-fixed-with-next-software-update/

Samsung's decision to stick with an ultrasonic fingerprint sensor is a unique one. Almost all the other OEMs opt for an optical sensor-based solution, which is not only quicker but also a tad more secure. To make matters worse, the Galaxy S10's fingerprint sensor didn't play nice with a lot of third-party glass-based screen protectors, much to the dismay of several users. It is because an ultrasonic fingerprint reader works by sound waves at the user’s finger and reading how those waves are reflected. The addition of a screen protector in between messes with the waves, causing the phone to misread fingerprint data.

Screen protector manufacturers worked around this by reducing the gap between the fingerprint sensor and the protective layer using a liquid adhesive. It does solve the problem as the phone can now be unlocked using the fingerprint scanner again. The problem is that just about any finger can unlock the phone, as was discovered by shocked users. It happens because the fingerprint reader is unable to read the finger’s ridges and pores clearly due to the layer of adhesive. The result is a not-at-all-unique dotted pattern that is saved as a fingerprint, allowing anyone to unlock your phone Samsung initially blamed the problem on the 'cheap' screen protectors. But the company has acknowledged it now and promises to fix it with a software update.