Offline reading doesn't always work. On the Mac I have to use the "save offline" menu. On iOS I haven't been able to find out when or why it does or doesn't work offline.
While it’s not on by default, there’s a Safari preference you can enable to save offline automatically: Safari > Preferences, click Advanced, then select “Save articles for offline reading automatically.”
Offline reading doesn't always work. On the Mac I have to use the "save offline" menu. On iOS I haven't been able to find out when or why it does or doesn't work offline.