Workaround until fixed: I re-paired all switches and re-configured them. Important thing to note: Open the official Hue app first and select “Configure in another app”, then proceed in Hue Essentials. This seems to work.
I don’t really feel like this problem is solved but I will close it nonetheless because a) there is an acceptable workaround and b) there are so many other issues with Hue Essentials that require more urgent attention.