When importing a contact record containing a multiple choice checkbox field, the number of ‘Options Per Line’ in the custom field definition also limits the number of options that can be imported for that field.

One of my WordPress/CiviCRM websites has a custom checkbox field with 13 options, with the number of ‘Options Per Line’ set to 3.  When I tried to import data for this custom field, CiviCRM would only import the first three options specified in the .csv import file, as if the number of items per line was also limiting the number of options CiviCRM would import.

A workaround is to temporarily set the number of items per line equal or greater than the total number of options while importing.  Once I realized what was happening, I changed the ‘Options Per Line’ setting in the custom field definition to 14, and successfully imported all option values even when all 13 were included.

I've only tested this on recent versions of CiviCRM for WordPress.