Change Tracking SYS_CHANGE_COLUMNS on Update operation

I would like to get an understanding of why on an update operation in the change tracking table, the SYS_CHANGE_COLUMNS can be NULL. I would expect the SYS_CHANGE_COLUMNS will be populated. In the example below, the first and second record's update has a NULL value on SYS_CHANGE_COLUMNS but the first record's SYS_CHANGE_VERSION SYS_CHANGE_CREATION_VERSION. The third record contains a value in the SYS_CHANGE_COLUMNS but the SYS_CHANGE_CREATION_VERSION is NULL. We use SYS_CHANGE_COLUMNS as a filter for updates to check if it is populated and it looks like we may be missing updates in this case. Any feedback on this is appreciated.