F5 requires IMDSv1 in order to initiate failover between two F5 devices. IMDSv1 is susceptible to SSRF vulnerabilities as indicated in the AWS document. If IMDSv1 is disabled in AWS environment for security reasons, F5 failover will not be seamless and the F5 logs will have errors like this:
err logger[15542]: /usr/libexec/aws/aws-failover-tgactive.sh (traffic-group-1): Instance sanity check failed with error:
F5 is tracking support for IMDSv2 in AWS internally using ID 968657