EC2 instance connect : There was a problem setting up the instance connection

Almost every time I've tried to use the SSH via Browser for EC2 never worked, like maybe 1-2 times, try to do it from terminal instead

In order to connect to your instance with "EC2 Instance Connect (browser-based SSH connection)" you need to install ec2-instance-connect to your AMI.

Try connecting to your instance via "A standalone SSH client" (eg. putty) and installing it with a command:

sudo yum install ec2-instance-connect

or (for Ubuntu):

sudo apt-get install ec2-instance-connect 

To me this worked, and I could then easily access my instance via browser next time.

The more detailed explanation is found here: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-connect-set-up.html

Ensure that AMI is of Amazon Linux 2 type as it comes bundled with necessary softwares. Recently there is a change in AMI selection window where Ubuntu is pre-selected.