Hi,
I need a few more details before I could provide my feedback.
One reason maybe the environment setup. If you connects your printer to router using USB and router to Mac machine wirelessly. In this setup, only printing works. And this is expected.
How do you do scan(using application or scan to computer)?
May I know which application do you used to scan? HP Scan? Image Capture?
When installing did you selects the correct driver and not AirPrint driver? During installation when adding the printer, AirPrint is the default driver. Make sure that 8600 driver is selected.