I received a call while phone screen was locked. The button to answer appeared but tapping it did not let me answer the call, why? How do I answer calls when the screen is locked? I have a similar issue with Bixby reminders and alarms. The reminder and alarm appear with a button to dismiss but tapping the button does absolutely nothing. I've had this phone just barely over 2 weeks and have had nothing but issues. It is the most complicated and useless and expensive piece of equipment I've ever had. I am so sorry I got rid of my S7.
Recent update (June 2019) did change answer and hang up button to require finger on button and slide right for answer or left for hang up. Most ridiculous update ever. Try it again, it will work.
It's been bugging me that I wasn't very clear. First off I corrected my signature to no longer say S7. Secondly, here is a screen shot of the interaction and dexterity screen on my phone. My phone is an unlocked version not associated with a specific carrier so it may be why our interfaces and options are different.