If you change the log level
gluster volume set myvol diagnostics.brick-log-level DEBUG
then reset the log level
gluster volume reset myvol diagnostics.brick-log-level
the process will continue to log at the DEBUG level instead of returning to INFO despite resetting the value in glusterd's view of the graph - removing it from gluster volume info.
This is fixed in latest releases (3.7 & 3.8) of GlusterFS with http://review.gluster.org/#/c/11887 , given that 3.6 will be EOLed once 3.9 is out (in another 3 months) do you see a strong reason to backport it to 3.6 branch?
This is not a security bug, not going to fix this in 3.6.x because of
If the issue persists in the latest releases, please feel free to clone them