Yep - thanks, kicked it now.
Background explanation: The app works by retrieving the list of new threads in the last 24 hours and scanning it for review threads, then writing the URLs of any it finds to a file - since it runs twice daily, that works out to continuously following all new threads in the forum. After a merger there are two valid URLs leading to the same thread, and there's no code in place to toss one of them in that case. There's ways to handle this (check for duplicate titles, or try to notice the redirect, etc.), it just didn't come up so far.