ECS Fargate task in private subnet can't reach another IP in private subnet

Hello,

I would greatly appreciate your input on the following issue: I have a Fargate task deployed in a private subnet with awsvpc network mode - which is successfully assigned a private IP within that subnet. Either so, I am not able to send requests to another service(EC@ instance) hosted in a different private subnet. A few facts:

1. The aws path reachability analyzer from the Fargate task container ENI to the desired EC2 instance shows a GREEN pass: so SG, NCALs and routing tables should be all in place - and working fine.
2. From the task container I am able to to reach the internet (NAT configured for the private subnet)
3. From a different IP within the same private subnet as the Fargate task container I AM ABLE to reach the desired EC2 instance which resides in the other subnet.
4. Routing table on the fargate task container:

Kernel IP routing table

Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0       172.31.64.1       0.0.0.0                   UG     0      0        0 eth1
169.254.169.254 0.0.0.0                255.255.255.255 UH     0      0        0 *
169.254.170.2 169.254.172.1   255.255.255.255 UGH   0      0        0 eth0
169.254.172.1 169.254.172.1   255.255.255.255 UGH   0      0        0 eth0
172.31.64.        0 0.0.0.0                255.255.240.0      U        0      0        0 eth1

I've exhausted all the troubleshooting ideas I had - and points where should I look forward?

I appreciate your help, John