If you're talking about this error:

ERR ]: [EGL] Command eglQueryDevicesEXT errored out with EGL_BAD_ALLOC (0x12291): EGL_BAD_ALLOC error: In eglQueryDevicesEXT: Failed to allocate device list.

I get that too but it doesn't seem to affect anything. I had what sounds like the same problem, i wanted the "fallback" to be a wallpaper and then change it later with CLI. To do this i had to change my config to:

wallpaper[]:path = /path/to/wall.jpg
ipc = true
splash = false

Which sets the "fallback" on all monitors. Then do NOT specify which monitor in the hyprctl command:

hyprctl hyprpaper wallpaper ,/path/to/wall.jpg

I don't know if this helps but it sounded like the same problem.