2nd Elastic IP access via SSH

Hello.
Are you correct in my understanding that you have followed the steps in the following document?
If routing and other settings are not properly configured, the ENI cannot be used even if it is added.
https://repost.aws/knowledge-center/ec2-ubuntu-secondary-network-interface

The following isn't completely clear:

both ips are in the same subnet and zone

This suggests to me these are private IPs within the same subnet of the VPC. But ....

i access server on first elastic ip, but not on the second

An Elastic IP address is a public IPv4 address https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-instance-addressing.html#ip-addressing-eips and the two that are assigned to your EC2 instance are unlikely to be in the same subnet (though it's not impossible).

Are you trying to SSH to public IPs or private IPs ? (Or it could be a BYOIP).

Separately, can you expand on what you mean by:

they share the same security group

When you initially create the EC2 and give it a security group, you're actually associating the security group with the network interface that's provisioned with the instance (the one you call eth0 so let's stick with that) and not the EC2. So when you create and attach the next interface eth1 it won't automatically be associated with any security groups.

Check that eth1 is associated with the same security group as eth0.

If this looks correct then go back one step to the host that is able to SSH to eth0 and check its outbound rules allow SSH to the IP of eth1, e.g. is the outbound rule tightly defined and only allowing egress over port 22/tcp to the IP of eth0 or something like that?