Unable to unblock a user. "We can't unblock this person at the moment. Try again later."

So I was struggling with this same issue and most of the options were iffy or required a few steps that weren't something that I could do on my end alone. So I tried simply unblocking via the Android version of the app and it worked immediately! I saw the user was removed from my desktop app and even after restarting the desktop app it was still gone and appears to be back to normal. Not sure what's different in the mobile app but it was an easy solution.