Photos won't import automatically
90% of the time when I take photos and plug iPhone into fire wire on iMac, photos import automatically in "Photos > All Photos" like they're supposed to.
10% of the time, photos don't import automatically (I have to click "iPhone > import" inside Photo app on iMac for them to import).
I don't use iCloud Photo Library; it is not clicked at "System Preferences>iCloud". But, failure to import photos sometimes seems to coincide with times my 5GB of free iCloud storage is full (with documents and desktop).
Why are photos not importing automatically 10% of the time? How can I get them to import automatically, without having to click "import"?
5yr-old iMac, 10.13.6 High Sierra. iPhone-6s
"Photo Stream" is turned on under "System Preferences>Photo".