Contacts sync partially
I am a new user and am trying to transfer my contact list from gmail to mailbox. Doing so, I copy a set of contact cards in my MacOS Contacts app from the google account to the mailbox one.
In the contacts app they look completely identical (even with the separate contact cards within the app).
However, when transferred to the mailbox portal, while I'm checking them, I discover lots of (seemingly random data) missing - most often phones, but sometimes other data.
Is there a robust way to ensure data transfer between MacOS (and iOS for that matter) contact data is transferred fully to mailbox?
I would not be able to use my mailbox contact list, as I'm constantly updating contacts on phone and/or laptop and need to trust replication fully, without fear of losing data.