Autosave breaks Fritz!Box's website

I tried this function with a new Fritz!Box login. I try to login with a new account that was never saved in 1Password.

After I enter the password and click on the login button, the login proceeds and a 1Password window appears sliding in with the "new item/update existing" function. However this immediately vanishes, when the Fritz!Box refreshes its content and displays the main page. I have no chance to choose anything from that 1Password window, and it's also not possible get this window again except by logging in again, but that's vanishing again as well.

The vanishing is so fast, I was only able to identify the sliding in window by recording a video and single step through the frames to validate it's really the 1Password popup.

I would like a function to manually invoke that vanished popup again. Or that popup should stay as long as I don't manually dismiss it.

This is a screenshot from that video, the frame before the popup vanishes: