A few hours have passed since I published and https://flathub.org/apps/me.sergiotarxz.JapaChar continues being a 404, other apps that got merged today do not have this problem.
It is still happening.
Yeah, caching might be a bit aggressive there.
If you try other languages it works Japachar auf Linux installieren | Flathub
It is working now, I am so glad it is not an issue because of my manifest or something like that.
I hopefully finally figured out how this happens, and it should be much more common now.
Much less I hope, I think you had a typo. 
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