The new reply in question was actually by Clorox_Cappuccino.Hello Kirazy,
You have a new notification on the Factorio Mod Portal.
New reply in Greenhouse by Kirazy.
You can see all your notifications, as well as disable them, on the Notifications page.
And all of my new reply notifications are bugged in this fashion.
Edit: Additional observations:
The links in the latest two new reply notification emails were to post #2 and post #5 in a given thread, both of which were received when the other commenter replied. Looking at the URL for the quote option, the index for quotes starts at 0, but the index for post starts at 1. Is it possible that the same index that specifies which post to quote is being used to generate post URLs and fetch author information?
e.g. This url https://mods.factorio.com/mod/reskins-a ... 69?quote=2 with quote index 2 quotes the post made by SilverNova115, which is the third post in the thread.
But the url in the notification email is https://mods.factorio.com/mod/reskins-a ... 769#post-2, which is the second post in the thread, but has the same index of 2.