EC2 instance was terminated, with new instance running, appears to be a problem with DB

For some reason, out of nowhere AWS autoscale decided to shut down our EC2 instance and a new one was launched, but now, even if our Backend is up and running on an ECS cluster container and the DB is running on RDS, there seems like our DB is unreachable, meaning on my website/application appears that the DB is offline. I have admin privileges, but I did not setup AWS, I just suppose to 'maintain' it and although im not completely clueless I'm not expert in the field. I'm unable to figure out what causing our issue. Security groups, and VPC are all setup correctly, havent touched it, all that got sorted automatically with the new autoscale group/template launch. If anyone could direct me or suggest some basic troubleshooting options(even though I feel like i checked most of them but still) that would help, would be much appreciated. Thanks, Csaba