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First, this topic contains serious spoilers so if you are not near the end of this game, you should turn around now.

I'm not really sure if this info is useful, but I've encountered this glitch and pretty embarrassed.
So I made my mind to write it down here so that everyone can see it.

The problem is about alternate ending.
If you gained enough core power to activate the system (at least 34) WITHOUT making contact with Sentients in the Helm, the Power Core quest, which is essential to the alternate ending, WILL NOT BE ACTIVATED.

To avoid this, try following solutions.

1.As soon as you have enough resources to open up Sentients' Pods, go to the Helm and make contact with them ASAP. This is the most important because I suppose you won't encounter glitch in this way.

2.IF you've already encountered the glitch, go to another habitat which is already in maximum bio mass level and contains couple of Phytas. Then kill Phyta with whatever you like to reduce the bio mass level from 5 to 4. After that, reproduce Phyta again so the bio mass level go back to 5.
Now, go back to the Helm and you might be able to get another signal communication from Sentient. He should tell you to go to the Power Plant. After you find Sentient at the Power Core, follow his instruction.
Be sure to use the left platform in the end.

Maybe I was so dumb encountering this glitch... Hope you guys won't!!
Hm, alternate ending? I thought there was only one ending. It seems I did experience this glitch. But how should I know? There's no hint of different endings, and now after 9 hours play I'm quite fine with the one I saw. Maybe I'll play again in some months (or years).

About glitches, there were indeed technical ones: sounds looping without any cause, graphical errors in videos, repeated words in dialogues. But nevermind, it is really a game with a very good story.
Thanks for the info.