Hi, Munso.
Simple scan can be fickle. I installed it on my wife’s laptop a while back and it never gave me problems. Then I installed it on my wife’s desktop and it refused to recognize the attached Brother scanner. I removed and reinstalled Simple scan using Synaptic about 3 times before it finally behaved. It could have been that some time in-between those 3 times I installed the manufacturer provided ubuntu driver that may have helped. But I recall that Zorin had automatically recognized the device without the manufacturer driver. So, I hate to say this but uninstalling and reinstalling is a tactic that worked for me. I also recall removing the non-CUPS device (same printer was listed under Settings->Devices as two separate devices after the manufacturer driver installation) and then the Simple scan worked.
On the other hand, you could try what is suggested here: https://askubuntu.com/questions/969238/samsung-m2070w-scanner-no-longer-working-in-17-10
I also recommend trying steps #4 and #5 (in my earlier post), if you haven’t already tried them.