Resolved problem by switching to geocoding
After several different attempts with using actual street address, I added geocoding to each address. Apparently Google maps was having problems with some of my address, and it repeatedly affected the reliability of the maps. Different refreshes would produce different pins showing up. I should add that the addresses were all European, and even after removing foreign accents, it appears Goggle's problems in finding the addresses cause problems. But switching from addresses to geocodes all of the problems disappeared immediately, and finally all the pins/flags/pillows were properly displayed.