Why am I only able to pass health checks on one instance at a time, but not both?

[MP32]

For some reason I can only pass health checks on one instance at a time, instead of both instances simultaneously. I have my instances deployed via an Auto-Scaling Group using a launch template. So they both use the same user-data script. Whenever I first deploy them only one will ever pass the health checks and the other gets a status code of 500. Here's the part that I don't get, let's say that when I first deploy the instances, instance 1A will pass and 1B will fail the ELB health check. I then stopped Jira on both instances, purposely started Jira on instance 1B first and then started it on 1A a couple minutes later- now my instance 1B is passing health checks and instance 1A isn't. It's like I'm only allowed to run Jira on one instance for some reason. How do I fix that?