I did bits of both: I used the tubing that came with it (the middle piece, the part that goes through the incubator lid, and the tube that hangs in the water) and I cut new (the tube that goes from the unit to the tube in the incubator). It didn't matter. None of the tube is kinked and there appears to be no holes in the tubes.
Yes the incubator was sitting in the slots properly. Heat-wise, it has been steady, and that shouldn't be true if the lid was off. Plus, because of the water at the bottom, the humidity stays even. It won't drop below the high 20's. It just won't go much higher than that.
The tubes were dry when I tested them for air holes so no water had gone through them.
But this is curious. You said: "I had the problem right away with that I used a piece I cut which was just a little bit to long and thus didn't work."
Are you suggesting the length of the tube was an issue? How long is yours, from the humidifier to the incubator? I guess that piece could be too long (since that is the piece I had to cut myself), but how odd. It would be nice if the instructions mentioned that possibility. Ugh. I am willing to try anything at this point though so what info you can provide would be great.
I don't remember the exact length, it says in the instructions somewhere, I can find out when I get home from work. But its also important that its not to short, I had a few problems with it snapping off (this was of course during lockdown and I was outside most of the day).
I know you said you already check this, but with the lid not being on properly, the temperature on mine was holding true, the humidity was just stuck at what my room humidity was.
Went through the same thing, I think everything that went wrong with my first hatch was humidity pump related. Tubing to short/long, snapping off, etc. On my second one now, and so far the pump is working great.