Opcache causes fatal error: Cannot redeclare class lesson in /var/www/moodle/mod/lesson/locallib.php on line 983

Fresh install of moodle v2.9.1+ from moodle.org

Gets the above error on what seems to be every configuration page.

I think there's an erroneous include/require somewhere, but I can't find where it is.

There have been several reports of this for the last few years, but as far as I can see, no resolution
https://moodle.org/mod/forum/discuss.php?d=244509
https://moodle.org/mod/forum/discuss.php?d=261606
https://moodle.org/mod/forum/discuss.php?d=263487

(I refuse to use the opcache.dups_fix=1 "fix" on principle, that's just not a solution )

Any ideas?