sftp permissions limited to primary group after update?

Question

My CentOS7 server runs sftp through openssh. Users are chrooted to a dir with subdirs that are owned by another user, but sftp users are group members through their primary or secondary groups with rwx permissions. Since a recent update they are no longer able to access folders owned by their secondary groups, but can access folders owned by their primary groups. I am suspecting an update of openssh to be responsible for this change in behaviour (6.6.1p1-25.el7_2.x86_64 to 6.6.1p1-31.el7.x86_64). Can anybody provide insight on how to troubleshoot? Suggestions on ways to solve this other than downgrading openssh (if that indeed is the cause)?