Load Balancer 2/3 connections from external IP fail

Summary:

Connections into load balancer fails for about 2/3 (67%) of connections made to its public IP from the internet.

Content (required):

A VCN has a public and private subnet. There are two private compute instances amd a private load balancer (layer7) in the private subnet. There is a public network load balancer (layer4) in the public subnet.

The private load balancer has a listener on port 80 connected to a backend set having two backends in the private subnet containing the load balancer. The backends are the two compute instances; they run a web server on port 80.

The public network load balancer has a listener on port 80 connected to a backend set with a single backend which is port 80 of the abovementioned load balancer's internal IP address.