Books <-> CRM synchronisation with custom Fields

Books <-> CRM synchronisation with custom Fields

Hello,

We are synchronising Books Customers with CRM Accounts.

In CRM Accounts I set up last year a "segments" multiselect field shown below


In Books, I set up a custom multi-select field with the same value as in the CRM


And set up the synchronisation inside Books. Want to synchronise the Books Segments with the CRM Segments, but the later doesn't exist, and another non-existing is there ?!


First, I don't understand where the field Segmentation is coming from.

Second, I set CRM Segmentation to sync with Books Segments, and after one week CRM Segments from most Accounts has been emptied!

I'm a bit confused how this synchronisation works, as other fields are working fine... Is there something I should take care of with multi-select field ?