Its happened a lot with me phone unlocked from it self in my pocket I have a70 so I hope Samsung add new option to make finger print work only if I wake up my phone so by this way it will not open in my pocket by mistake.
no I dont have trusted device but I found the problem that if your screen touch anything like tissue and you fingerprint was printed in the screen it may be unlocked the screen I tried with my self many times and its unlocked so I believe to fix this...