But look at this, it's the ScriptColumn.multicol description from the docs.
It shares my point of knowledge, it explicitly tells that it's not required to provide values for all the columns in the multicol set.
[quote]If your script implements multiple columns that require common calculations to perform, you may wish to set the multicol property. If this is set to True then your column handler function has the option of returning data for multiple columns simultaneously, rather than just the specific column it is being invoked for.
When your handler is called, the ScriptColumnData object won't contain the usual group, sort, type and value properties. Instead, it will have a columns property that points to a Map that lets you set the values for one or more of your columns at once.
...[/quote]
Whatever the result of this confusion will be. I just checked another column script where values are missing dependent on where the column is positioned and it seems the issue also happens for single type columns. So this multicol fact might not be relevant here.