I encounter the same problem as it looks like.I had lots of (13: Permission denied) entries in /var/log/nginx/latest.log and after altering the rights of the /var/log/nginx folder those entries were gone and log lines were stored properly in the belonging log files.You wrote that the /var/log/nginx rights were root:wheel that differs from mine which were root:staff.Log entries are written by nginx as user www which is as expected. I haven't tried a reboot yet but if the case is that this is changed back after every reboot that would be very inconvenient.