Assigning it to engineer responsible for upgrade script. In a fresh 3.1.x there is no issues with updating clients.
It seems script doesn't add new attribute for clients to schema. Here is workaround you can use:
/opt/gluu/schema/openldap/gluu.schema. Add attribute definition like this:
attributetype ( oxAttribute:375 NAME 'oxDisabled'
DESC 'Status of client'
X-ORIGIN 'Gluu created attribute' )
Add the new attribute to the objectclass 'oxAuthClient' in the same file; you'll see there a list of attributes separated with "$" sign
Make sure your edits didn't break schema:
# /opt/symas/bin/slaptest -f /opt/symas/etc/openldap/slapd.conf
# service solserver restart