In my experience, this is how people react to pretty much any rng in any game. You always notice the bad rng more than the good rng so it always looks like the rng is skewed against you beyond what it claims the probability is.

And as always, the only way to be sure would be to test it hundreds of times and record all the results to see if it actually does consistently deviate from the expected results.
(or, in this case, somehow find the formula in the game's code to verify it)

first one I saw I was all about putting an outpost on it...!
I dunno every one I have done which is < 10 and 0 since H&H ... they let you get about 5 nodes then sink, which is enough to make a harpoon and a knife. I collected extra for later just in case, and stopped bothering. This is one of 3 or 4 crafting material that needs to be used in more stuff (cough, core wood).

It does seem like I get more than 20 seconds between the cry and the sink but I'm not sitting here with a timer to verify it so it could just be that panic mode makes the time seem longer. At this point I start with the barnacles furthest from my boat, when they cry out I move to the barnacles closer to my boat, and I don't tend to hop off until the actual bubbling starts. I would believe it's 20 seconds from the bubbling to the sinking, but it seems like more than 20 seconds in total.

I've so far gotten enough this game for the harpoon but I'll still need a bit more for the knife. I get that it's rng based and I could just be unlucky or dealing with observers bias, that's part of why I asked the question. I do think at least part of it is my poor luck though. I tend to have weird luck in games, it's amazing when it counts and I survive things i really shouldn't, and horrible when it comes to just general mechanics like spawn rates or the sink in this case. Like this leviathan hunt started as a serpent hunt but I had better luck finding the leviathans since they just sort of pop into existence in front of my boat and I nearly crash into them, but considering I am hunting serpents, sure lets go ahead and get the tool that makes it easier to get their scales compared to kiting them into shallows (even if it's mostly meat I'm after).

Yeah it's luck, I've been able to get every barnacle and didn't cry once. I've been able to mine once and it started to cry lol

Yea I think the wiki is wrong if they say it's 10%
I think they've started crying after one hit everytime for me. I do believe though that I sometimes had more time between first cry and the plunge. But I'm not sure, I haven't harvested enough barnacles to say for sure (you only need so many)
Unrelated but I cease the occasion to brag about this one
https://steamcommunity.com/sharedfiles/filedetails/?id=2622476737

There appears to be some RNG involved. I've only encountered 3 leviathans, but all since H&H update.

My experience has gone one end of scale to other -
1- first ever encounter, didn't even know what it was, had to google it afterwards. Luckily didn't die but as I mined the barnacles, got like 6-7 of nodes before it started sinking,

2 - this one I thought was bugged because I literally mined almost every single barnacle on it, until the very last one then it started sinking. I managed to pickaxe that while sinking and swam to boat which I now learned to always park with ladder side facing you if using karve.

3 - this one sank really quick, barely after getting first cluster of 4 barnacles

So while my xp is limited, seems like there is some kinda RNG roll on when it sinks.