This is for sogo-connector 31.0.4. In

chrome/content/sogo-connector/addressbook/common-card-overlay.js

there is this code segment:

/ migration from MoreFunctionsblabla /
let cardCategoriesValue = gEditCard.card.getProperty("Category", "");
if (cardCategoriesValue.length > 0) {
let migrationValue = cardCategoriesValue.split(", ").join("\u001A");
gEditCard.card.setProperty("Categories", migrationValue);
gEditCard.card.setProperty("Category", "");
}

As you can see, if there is some value in the "Category" property, it will be moved into the "Categories" property OVERWRITING any value present there.

If a user happens to use both properties, he will lose data without any notification or prompting. I have a pull request open for this, but it has been ignored so far:

https://github.com/inverse-inc/sogo-connector.tb31/pull/26

My suggestion is, to remove the auto-migration code, as you do not know, if the user wants to migrate or not.