Do you have navigations bar disabled?(swipe gestures for home, back and multitasking)
And if you do have the bar enabled try downloading Good Lock off the Galaxy Store, and in the app download the Task Changer addon.
Same issue with mine.. Stopped showing after last update.. Doesn't show up when using full gestures, but shows up when I put it on navigation button.. I've contacted Samsung and they tell me to use the stock launcher 🤦🏾♂️🤦🏾♂️🤦🏾♂️ I guess they not trying to fix it or don't care 😔
I've noticed this issue back in the Note 9 and it carried over into the Note 10 as well. My work around is to launch Samsung Pay from the lockscreen as it seems to always be present there.
I had this problem, too... It turns out it was Greenify turning the app off! If you have an app like Greenify installed, to hibernate apps more aggressively, make sure that Samsung Pay is not on the list of apps that it controls! I wanted to out this on here because I fiddled with various phone settings for 2 days trying to fix this issue. I actually just uninstalled Greenify because I feel like my phone has enough settings to optimize apps, and battery life is not a big concern yet. I'm using the note 10 plus.