You have to be naked and wait a little, it takes some time to trigger
Well, I've figured it initially. But it turned out to be a bug in the end. There is an option in the settings to disable grapples (I suppose? Looks like monsters won't rape you while you have HP). I'm not sure if it was this way by default or I've toggled it for a smoother gameplay a while ago and forgot. Anyway, the bug is in the inconsistency: this option normally doesn't affect tentacles, facehuggers, etc. (probably because grapples are their main purpose), except this last tentacles. I had to find a way to debug the game to figure this out.There are multiple trigger points that look like a platform from the turret boss.
and you have to be naked to trigger it. Funny thing about this fight is I often get tunnel vision and while I running around in the room to avoid the attack, I often stop and stand on these platforms and "accidentally" trigger the H scene.