UI - All scenes except one don't receive any input

Unity Engine
1

I have a number of different scenes, some of which contain UI elements. Though the UI in my main menu scene works (receives mouse input, basically), none of my other scenes seem to be able to receive mouse input.

This is especially confusing because, as far as I can tell, the two EventSystems are configured identically:

6974645--822524--upload_2021-3-25_15-51-21.png
6974645--822524--upload_2021-3-25_15-51-21.png714×699 55.9 KB

As are my two Canvas objects:

6974645--822527--upload_2021-3-25_15-52-49.png
6974645--822527--upload_2021-3-25_15-52-49.png712×897 66.6 KB

(The Sort Order is the only difference there, and I’ve tried changing that - plus, these particular canvases aren’t loaded at the same time)

UPDATE: After some experimentation, I have found that starting the end credits scene in isolation will make its buttons work. However, opening the end credits scene from anywhere else, even if the scene is open in isolation at the end of the process, still does not work. Does have multiple EventSystems in the scene at ANY time, break the EventSystems permanently?

2

Update 2: I’ve worked around the issue by creating an “Event System Smart Spawner” script, placed in each scene in place of all EventSystems, which spawns an EventSystem prefab, but only if none exist. This fixes the issue, and all buttons work again. This really feels like a Unity bug, though, there is absolutely no reason that an EventSystem (which is required to be in EVERY SCENE with a UI) to just flat out break if a second Eventsystem exists for a single frame.