One more to add :

... it gained round about 500 XP more than the other 4 i adopted bout the same time and equiped them all with the Lava Lamp in one day.

...well just if it helps in any way to find that bug.

My Air 14 knuffel leveled up from 27 to 28; the next time I clicked on her, she went from 28 to 32.

I do switch between my phone to my computer quite often; I fed my knuffels and went digging with about half of them (including the affected knuffel) on my commute home, then finished digging and fed the knuffel at home at my computer, at which point I got the level burst. Is it possible it might have something to do with having sessions open in several browsers?

This one

is the only one from my knuffel that has had a sudden growth spurt.
Not only once, but multiple times it happened that while feeding the red writing saying 'Level up!' appeared and I clicked on her and the normal level up screen appeared, wanting me to choose the element... but after doing that, exactly the same screen appears again! Most of the times it happens twice (and only once a day).
But I doubt that someone feeds her or that she gains as much exp for this to happen that often. Also, this is something that occured only recently.

It also happens to one of my knuffel:

Today it showed that he has leveled to 20, but when I clicked on level up to choose an element, the site kept reappearing and now he is level 24.
It has happened before for this knuffel (jumped from level 11 or so a few levels). All the other knuffel I bought around the same time are only level 5.
Posting this as more data might help you find the cause.

Edit:
And it just happened again. Reach level 25 and it somehow jumped to level 30. (March 20th)

this is happening to me RIGHT NOW !
it's kind of frightning and nice both at the same time

Man, why doesn't this happen to me??
I've had some sort of super fast level ups from time to time, but mainly cause I hadn't clicked on them when their level went up (you know, when you choose the element for digging exp) and since they continued gaining exp, when I finally clicked on them they immediately went up 2 or 3 levels.

Well to me most times it happens when i adopt multiple knuffel (4, 5, 6 etc...) the same time.
Almost every time there is one baby that gets this mysterious boost then and it continous till Lv.100.

I just had this happen to my Darkness Gen 8 Knuffel. I gave her up for adoption and then re-adopted her day before yesterday (Sunday?). She was at level 3 when I started digging tonight and now she is up to level 17 and still going. My Darkness Gen 16 Knuffel did kind of the same thing. He is level 100 right now and the Knuffel I adopted just before him is level 83.

EDIT: My Darkness Gen 8 Knuffel stopped at level 22.

it's happening to one of mine too... he's the same level as a knuff i've had much longer, even though i feed/play with them all the same amount.



he jumped three levels after today alone. ;n;

it used to not happen at all, and this is the only one affected.

This just happened to me as well! I have some documentation of it if a staff member needs it. I was actually just going to PM a mod (though i don't know if it's who I'd send it too?) about it because I was sure it was too sensitive to post here. But since it already is, I'm sharing my story.
This was originally written to be sent to a mod, so there are references to "you" and "you and the staff" but I don't see the need to edit it.

I leveled my knuffel, Keikeelee just a few minutes ago, from level 24 to level 25. I received the usual compensation for that upgrade as well as the picture change and the new element point, but then the "level up!" wouldn't go away. I kept clicking the element I wanted to select for her, and I suddenly realized she was getting higher and higher until she was level 32, all without me doing anything but clicking the elements again because I thought it hadn't applied. I documented the time, date, and level that she was at in a screenshot [which I can send to you or the staff if needed], and showed that I could level her within seconds again in another picture.) Then I refreshed, and the problems were still going on. I did a hard refresh and same. I was able to still upgrade her to level 34!
I'm fairly certain I could still upgrade her as far as I wanted (which was really, really tempting! :P) but I didn't want to exploit this.

Staff:
Let me know if you need my pictures as proof! I doubt you would, but since it's still not resolving itself, I'd be happy if I helped. They really don't have much other than showing it happened within seconds but it might be useful...?