AWS hosted sites like slack unreachable

[Margi Varia via NANOG <nanog () nanog org>]

Hi Nanog,

We are seeing this weird issue in one part of the network. Customers in one public subnet are not able to reach certain 
websites suddenly which are hosted in AWS like slack.com, bill.com..

We changed the subnet to new one and issue resolved, after 48 hours, we have the same issue again. We are not AWS 
customer, so can't call them, but what are our options?

Thanks,
Margi