Abyss opens without stepping on the crack

The abyss opened for me by itself twice in about 5 minutes. It happened to me also the other day, same place. Everything around the solaris palace in act 3. I don't think this feature was intentional.

Same happened to me but not specifically in Solaris.

What seemed to happen :
I step on the hidden hole where rare Abyss monsters will spawn and it opens the hole, releasing the Abyss rare monster. But it did not trigger the Abyss event.
So if you don't rush to trigger the Abyss event, you will fail the Abyss because of the time limit.
And as the holes are invisible before the Abyss event is triggered, you can step on the final hole (or any intermediate hole) without noticing it... :(

Happened to me too few times today in various ACT 8 zones.