The Game Master's notification page didn't work on it's own, so I looked into it.
Let's compare the HTML source. This is what I'm looking for:
Notifications
<div class="post">Notifications: <a class="ul" href="
And this is what The Game Master produces:
Notifications
<div class="post">Notifications: <a rel="ugc" class="ul" href=
There's an additional
rel="ugc", and I don't know why. So my solution is to just removeo that code tag, and it works again

I may have found a solution using notification bots.
I created a new account:
The Game MasterFor each round, participants can make only one prediction by tagging The Game Master.
If they forget to tag TGM, their prediction will not be valid.
Proof of their prediction will appear, for example, here :
https://bitlist.co/user/id/3763375/notificationshttps://loyce.club/notifications/3763375.html (when it works)
It doesn't make a big difference, but
This prevents multiple last minute ninja edits.
It’s still simple.
I’m afraid a lot of people will forget to make their predictions (I will try to send a reminder 24 hours before the prediction period ends).
The predictions will be public, so those who make theirs last will always have a slight advantage.
Don’t mess up your prediction (don’t forget a 0, for example).