@Keerthika Selvendran 20230000121-MSP01 ,
Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.
I understand that you are using the feature AFD Premium with an internal load balancer origin with Private Link and experiencing occasional 404 issues.
The only way to check if the 404 occurs at the origin (ILB) or the AFD is to check the AFD Access logs.
Please share the entire log (All fields) for when the HttpStatusCode becomes 404.
See : How to Configure Azure Front Door logs
Cheers,
Kapil