When I step on the Celestial Gateway, everything works as expected.
I just broke it (using a Tinker's Hammer) while standing on it. The sphere disappeared, but the dark effect is still here, so I can not see anything.

Mod Version "1.12.2-1.8.10"

I can not give any more information, I guess, but I hope this still helps.

Why did you do that?

Because I wanted to move it.

Was it broken using the center of the Hammer's area, or the edge?

So, I was standing on the center, moved about a block (I still saw the sphere).
Then I used the Hammer to remove one corner of the ground.
The center of the Hammer was here:

XXXXXXX
XOXXXXX
XXXXXXX
XXXXXXX
XXXXXXX
XXXXXXX
XXXXXXX

After the 9 blocks were mined, the sphere disappeared but the world still stood dark.
(I checked twice, it was in the middle of the day)

It disappears when moving away from it or shortly after breaking. If not, then the hammer doesn't cause tileentities to disappear on clientside which is a big problem and should be reported to the respective mod doing the blockbreaking.