A ‘soft bounce’ is generally a delay in delivery. They often happen if many emails are sent to Gmail addresses in a short time period, or there were a lot of links in the email message, or your email ‘authentication’ needs to be improved.
Have you setup ‘custom domain verification’ within your Mailchimp account? If you haven’t that will really help as it verifies email sent on your behalf through Mailchimp is legitimate (not spam).
I had a look at your ‘SPF’ record (your IT folks will know what that is) and it doesn’t include some things that MailChimp needs… more info here: Set Up Custom Domain Authentication: DKIM and SPF: https://eepurl.com/dyimHv
We use Campaign Monitor and find it to be reliable for delivery. These days, with most systems, you will need to setup ‘domain verification’ for bulk email to be delivered reliably.