We have the same issue here. This issue has also been noted several times here in the forum e.g. here Reviewer reminders
This is definetively and important issue, leading to confusion and to incorrect e-mails to reviewers. In one of our journals on our platform several reviewers have already complaint about this.
Just to sum up the issue: If I click on the “Send Reminder” link next to a reviewer which has not acceppted a review - to remind him, to acceppt or decline the review - the e-mail-template REVIEW_REMIND or REVIEW_REMIND_ONECLICK is shown and sent to the reviewer, if you click on “Sent Reminder”.
It would be much better, if an email REVIEW_REQUEST_REMIND or REVIEW_REQUEST_REMIND_ONECLICK could be sent. There is not such a template yet, but there should be one.
Of course you can correct the e-mail manually before you sent the reminder to the reviwer, but this is really inconvenient.
@asmecher, can you have a look into this issue? It would be great if PKP could fix or improve this.