Serafina and Splinter, Have you tried to call Apple Care (1 800 692 7753 in the US) I think they also have So America numbers but not sure. I just use WiFi calling. Sometimes they try to charge you when you are out of warrantee but mostly not, especially if it is a software/OS problem. I just got off an hour and a half call with a second tier specialist trying to figure out why disk 1st aid isn't working properly. We finally sent data to the engineers and she will call me back on Friday with answers. I also asked her about some problems with Photos. My Mac is a 2013 MacBook Air, out of warrantee.
High Sierra was a major change in the OS and knowing the details is way above my pay grade. It did affect how pictures are handled. I think that when doing OS upgrades you do have to do a little research to see if there are any known problems. MacWorld.com and iMore.com are good sites.