I just ran a test: once the reviewer check “I may have competing interests…” and specify a reason in the textbox below :
This comment/reason is not recorded into the database (review_assignments.competing_interests) if the reviewer then decline the review request…hence nothing can be shown to the editor.
At best, he/she could add or copy/paste the CI comments in the textbox that will be sent by email to the editors…say after the default text maybe ?.. (shown after clicking “Decline review request”):
I would agree with you that the CI comments/reason should be logged and shown somewhere to the editors even when the reviewer declined the request (that could help prevent some other subsequent irrelevant review requests and/or provide better information/context to the editors).