I think my issue my be a different one perhaps:
╰─λ hyprctl monitors
Monitor HDMI-A-1 (ID 0):
3840x2160@60.000000 at 0x0
description: LG Electronics LG TV SSCR2 0x01010101 (HDMI-A-1)
make: LG Electronics
model: LG TV SSCR2
serial: 0x01010101
active workspace: 1 (1)
special workspace: 0 ()
reserved: 0 40 0 0
scale: 1.00
transform: 0
focused: yes
dpmsStatus: 1
vrr: 0
This is my current monitor setup
monitor=HDMI-A-1,3480x2160@60,0x0,1
The weird bit is the hovering of waybar fixes it (and, yes if I remove the waybar from the top, I can no longer it to break the black screen)
I have created a github issue here