Keep Your Record Type Value Settings When You Convert a Custom Picklist to a Custom Multi-Select Picklist
We enhanced the conversion of a custom picklist field to a custom multi-select picklist
field to preserve an associated record type’s value settings for the field.
When you work with record types and convert a field from a custom picklist to a custom multi-select picklist, your record type value settings for the picklist field apply to the new custom multi-select picklist.