Ok let me ask in different terminology.

is agent running on your instance1 host. What is that host.
Suppose instance1 is running on XYZ host.

Then does that XYZ host and Agent XYZort are showing up on EM.

if yes can you do "emctl upload" from that host.

Also check if you can do

sqlplus dbsnmp/xxxx@ or tnsping instance1 from instance1 host do you get same ORA-12170 error.

Is your DB and agent are installed with same user.