thank you Derrick! I have some more info from our end..
Unfortunately, we've had no luck getting this site recognized as secure on any browsers. We were able to identify one IP address associated with campyellowjackets.com (198.185.159.144) that shows up on a DNS blacklist (likely reported at some point to be scam/spam). It's possible this is causing the issue, but it's hard to say for sure.
All the necessary DNS records and SSL settings are in place and seem to be consistent with other live sites hosted on Squarespace we manage. This issue seems directly related to the campyellowjackets.com domain name.
Would contacting Squarespace help to help associate that domain name with different IP addresses that have not been flagged?
The email address we registered the domain with (domains@kampgrizzly.com) is not listed on any blacklist that I can find. I don't believe it's related to the issue.