A couple dozen of my domains have been migrated from Google Domains to Squarespace. The experience has been seamless so far. All the settings have been retained and the UI is very good compared to other registrar UIs out there that look dated.
Your description is confusing to me. A domain migrated from Google Domains to Squarespace retains its zone in Google's Cloud DNS service. In other words, there is no DNS zone migration. The name server entries on all of my migrated domains are *.googledomains.com. If you're saying that Squarespace is having DNS propagation issues for your migrated domains, then Google Cloud is having propagation issues on the Cloud DNS service. We would have likely heard about that in a separate HN thread. But it's not happening. My migrated domains are propagating edited entries just fine.
I think the issue is the connection between the squarespace management UI and the google DNS service - they probably are not successfully sending your changes over to google which is why nothing is updating. I'm having the exact same problem as OP.
Your description is confusing to me. A domain migrated from Google Domains to Squarespace retains its zone in Google's Cloud DNS service. In other words, there is no DNS zone migration. The name server entries on all of my migrated domains are *.googledomains.com. If you're saying that Squarespace is having DNS propagation issues for your migrated domains, then Google Cloud is having propagation issues on the Cloud DNS service. We would have likely heard about that in a separate HN thread. But it's not happening. My migrated domains are propagating edited entries just fine.
Did you find the actual issue on your domain?