Check the dev console ignoring the resource cache when loading pages,all network requests status are 200.
Verified this bug.
Safari Version 11.0.3
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.