Sharegate displays the following error:
Drafts owners cannot be preserved, therefore drafts will only be visible to the approvers and not anymore by the authors of the files.
Even if Sharegate is able to preserve authors and timestamps, drafts owners cannot be preserved. As a consequence, after the migration only the approvers will be able to see the drafts if the draft item security is set to 'Only users who can approve items [and the author of the item]' in the destination list settings. Authors of the files will not be able to see the draft files anymore.
To allow contributors to see their drafts after the migration, you can change the draft item security in the list settings to 'Only users who can edit items' or 'Any user who can read items'.