“fieldset.hidden-fields-container” appearing after recent update

Hello, I have a form with fields visible/hidden conditionally, and after some recent releases (not sure which one), I see now this additional field displayed.

When I check in the Inspector, I see “fieldset.hidden-fields-container” but it doesn’t correspond to anything in my form, and I have not done changes in my form for a very long time. Any idea what this is? I thought to just add a “display:none” but that wouldn’t be very clean…

Video : https://jeriss.tinytake.com/msc/MTA5NDU2NTFfMjQ2NzAwMTc