The problem is, that the URLs are saved urlencoded in the database, and are urldecoded in the backend, but not when redirecting. It should not urlencode them when saving, because this breaks backwards compatibility as well.
So & are saved as & a m p ;
(without the spaces, the forum is also buggy here) which breaks affiliate links with parameters.
So quickfix is to fix the links in the database and not editing any more links in the backend until the plugin is updated. Ideally the update would recognize broken links and urldecode them and save them correctly when called.