Filter VPC flow logs to check connection between RDS mySQL and EC2

Connection between database and EC2 instance breaks at random times, even if there is 0 traffic and I have enabled VPC flow logs to figure out why. I can't seem to filter logs related to my RDS instance. I have tried filtering out logs according to my EC2 instance id, [let's say Instance ID is a123 and the filtered-out logs contain another instance ID, let's say b456 this is my custom flow log format: ${instance-id} ${srcaddr} ${srcport} ${pkt-srcaddr} ${pkt-src-aws-service} ${dstaddr} ${dstport} ${pkt-dstaddr} ${pkt-dst-aws-service} ${flow-direction} ${traffic-path} ${action} ${log-status}] and also port that my RDS instance uses, but it is not working.