Bug  16339963 for the get-ostype has been filed for situations where your agent discovery show your instances as known but  the targets are not captured by the agent

cd <AGENT_BASE>/plugins/oracle.sysman.db.discovery.plugin_12.1.0.2.0/discover/utl
cp hostCompareUtil.pl hostCompareUtil.pl_orig

Edit the file hostCompareUtil.pl

my $OSNAME = emdcommon::get_osType();

to read

my $OSNAME = get_osType();

Bounce and resync your agent