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.