É porque os servidores DNS do AWS ELB retornam um CNAME diferente para cada consulta sua com políticas específicas próprias. Pergunte à AWS sobre possíveis CNAMEs e, quanto ao seu domínio, eles retornarão.
# host -t ns crashlytics.com
crashlytics.com name server ns-279.awsdns-34.com.
crashlytics.com name server ns-1609.awsdns-09.co.uk.
crashlytics.com name server ns-1226.awsdns-25.org.
crashlytics.com name server ns-968.awsdns-57.net.
# host -t cname e.crashlytics.com ns-279.awsdns-34.com
Using domain server:
Name: ns-279.awsdns-34.com
Address: 205.251.193.23#53
Aliases:
e.crashlytics.com is an alias for events-endpoint-b-1623273513.us-east-1.elb.amazonaws.com.
# host -t cname e.crashlytics.com ns-279.awsdns-34.com
Using domain server:
Name: ns-279.awsdns-34.com
Address: 205.251.193.23#53
Aliases:
e.crashlytics.com is an alias for events-endpoint-455714294.us-east-1.elb.amazonaws.com.