Here is how to solve it once and for all. The problem has to do with a synchronization fault in contacts. I couldn't find any online solution that worked (e.g., disable Samsung Pay, clear the cache, Master Factory Reboot, etc.), so I had to figure it out myself. The reason some of these appear to work is that, until you expressly add the account back that's causing the problem (see below), everything will be fine. But once you add that account back, the problem resurfaces.
1) Go to Settings->Applications->Contacts
2) Select CONTACTS TO DISPLAY
3) You will see a rather long list of choices. The default seems to be the first choice, i.e., All Contacts. When you choose this, then Android tries to sync your contacts from everyone: gmail (every account you have), Samsung, Facebook, Outlook, Skype, LinkedIn ... and this is what is failing. Given the combinatorics of the operation, it's not hard to see what this would be inherently buggy.
4) You have a few choices now, but ALL CONTACTS isn't one of them. In my case, I keep all my contacts in a particular gmail account of mine. So I selected only that account. Problem solved. Alternatively, if you scroll down to the very bottom of the list, you'll see the choice "Customized List." There is a little gear next to it. You can click on that gear and then choose whichever particular accounts you want synced. This will be trial and error. Start with one. If that works, add another -- if and until the problem recurs. For me, it's a lot easier to keep all my relevant contacts in one particular gmail account, but this provides you with a way to sync more of them -- if you insist. Eventually, you'll find out which account(s) is (are) the troublemaker(s) and you can exclude it (them).