It seem like a change in the handling of custom field types, there has been an internal change in CiviCRM 5.27. Multi-Value fields used to be marked by the html_type "Multi-Select" (and two more "Multi-*").
With 5.27 the html_type was always set to "Select" and the serialize flag was used to mark multi-value fields.
They have added some compatibility code to provide a legacy API (v3), but they didn't cater for html_type search parameters. Therefore XCM doesn't detect these fields as multi-value, and ignores them.
It seem like a change in the handling of custom field types, there has been an internal change in CiviCRM
5.27
. Multi-Value fields used to be marked by thehtml_type
"Multi-Select" (and two more "Multi-*").With
5.27
thehtml_type
was always set to "Select" and theserialize
flag was used to mark multi-value fields.They have added some compatibility code to provide a legacy API (v3), but they didn't cater for
html_type
search parameters. Therefore XCM doesn't detect these fields as multi-value, and ignores them.See CORE-1996