SES managed dedicated IP pool uses IP address that is bounced by Microsoft domains like Hotmail, Live, MSN, Outlook, etc

When using a managed dedicated IP pool for mailings, the emails using Microsoft domains (Hotmail, Live, MSN, Outlook, etc) are soft bounced with the following error message:

Action: failed
Final-Recipient: rfc822; xyz@hotmail.com
Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [54.240.53.199] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [BN8NAM11FT015.eop-nam11.prod.protection.outlook.com 2023-07-17T15:04:32.309Z 08DB86C8320E9038]
Status: 5.7.1

Apparently the IP address 54.240.53.199 that was assigned automatically to our managed dedicated IP pool is blocked somewhere.

According to https://multirbl.valli.org/lookup/54.240.53.199.html the IP address is currently on 9 public blocklists.

My questions:

1. why are IP-addresses used that are on (public) blocklists? We choose using paid managed dedicated IP pools to prevent exactly this...
2. we sent one mailing at 17:00, resulting in hundreds of soft bounces in a few minutes by an "important" party like Microsoft due to use of a blocklisted IP. One hour later at 18:00 we sent another mailing which also resulted in hundreds of bounces since the same IP was used. How "managed" is this IP-pool? How do these bounces affect the used IP addresses? Isn't there some kind of mechanism that rotates the IP address when hundreds of bounces occur within minutes?
3. what to do in such case? Open a support case (I did, they referred my to asking the question here...)