Now using the Simply Pay function and that def simplifies the process. I had turned this off as soon as I installed SP.
Sometimes, my fingerprint just doesn't read in Samsung Pay - maybe it's because when on-the-go my thumbprint may be unlike the freshly-scrubbed, totally dry thumb I used when setting it up. But, I don't seem to have any issue though using my print to simply access the phone - which doesn't make sense since it's the same fingerprint engine at work. So I now have a handy PIN set up.
Also, regarding transaction success, it might be totally random, but now that I don't use my MC on SP any longer - I only use my Chase Visa - every transaction is quick and 100% successful. Not sure if card type is a variable here, but for me, it sure looks like it might be.