Cert errors accessing s3.amazonaws.com from backup software

We have nightly backups which point to a bucket in S3.  The traffic leaves the VPC via the UTM.  Ever since I enabled Web Filtering with the defaults except for blocking a few categories, my backups periodically fail with certificate errors.  see below for sample errors.  So I have tried adding domains like s3.amazonaws.com to the whitelist which I thought helped but then another error would show a different IP. When I did an NSlookup on that IP I get another flavor of amazonaws.com like 1-s3.amazonaws.com.  I did check include subdomains in the whitelist.  

I then tried adding IPs and Domains to Filtering Options and marked them as Trusted.  I am still getting the occasional failure though.  Can you tell me if I am working in the right direction?

Thanks in advance.

Peter

“Content blocked While trying to retrieve the URL:https://52.216.65.179/ The content is blocked due to the following condition: The URL you have requested is blocked by Surf Protection. If you think this is wrong, please contact your administrator. Report: Blocked Category (Uncategorized)