In my experience, we need to migrate to 1.7 first in order to move all attachments from file system to database , if you go directly from 1.6 to 1.10 , attachment might be missing.
We need to run the following queries before to fix some issues with database:
ALTER TABLE `supportedf_help_topic` ADD INDEX(`topic`);
ALTER TABLE `supportedf_department` ADD INDEX(`dept_name`);
If you have duplicate topic you might need to clear the topic first
TRUNCATE supportedf_help_topic;