I'm pretty sure I have figured out what the issue is. Thankfully, it wasn't an issue at all, rather a new member posting what I consider spam. He/she signed up and all they did was send a PM to me and like 9 others asking the same question that they asked me on youtube multiple times. I just deleted the PM he sent and thus, when clicking on the link in the email for the members that were included, it would toss a 400 error.
But like I told Jared in the PM we created together to test this, I would rather have a member say he thinks there is an issue and there not be one than having an issue and not reporting it. Kind of like the Account Upgrade link going away after the latest update that I didn't know about until a few days ago lol. Thankfully that issue has been resolved now as well.
Thanks for bringing this to my attention Jared!