Both of those URLs with the query params before the #! do not send me to a 404 page.
It’s correct for us to have those query params before the hash fragment, it’s the URI standard and we’ve seen remix links being broken when we had params after the hash fragment otherwise.
By the way, I had only tested your app’s button, and the links you copied in your thread here, on Chrome. I also just tried it on Firefox and didn’t see any 404s there either.
(It’s probably not even a problem for us to remove those query params anyway since we don’t use the button anymore, so I’ll look into that…but that doesn’t solve why those pages are 404’ing for you!)