AWS ECS issue with cloudMap service

i have created an ECS service and during creation i have enabled service discovery, which in its turn create a namespace in cloudmap service, then cloudmap have created a hosted zone in Rout53 for the ecs service, then i have used that cloud map provided dns name as a CNAME to my domain sub.example.com which is located in different hosted zone,

**Issue: **

the above solution was working since about 1 week but i noticed that this solution was not work any more yesterday.

To solve the issue temporary, i have mapped the EC2 instance ip (which created by ECS to hold the ecs service) to the domian instead of mapping the domain to the cloudmap DNS service, and everything is working properly,

so i don't know why this issue happened suddenly, all things was ok till yesterday, but something unexpected got happened with the cloudmap dns which was working before with no issues.