Optifine HD C7 Ultra
forge-1.12.2-14.23.1.2555
LLOverlayReloaded-1.1.4-mc1.12
It seems the mod has problems with certain shaders, where no overlay is visible. I'm not really sure if it's the mod itself or the shader.
For Example with SEUS 1.0.0:
Screenshot
Strangely the overlay is only visible on blocks higher then the level I'm standing on. Every block above shows the numbers.
With Sildurs Vibrant Shaders v1.166 Extreme the overlay is not visible at all