[MikkiJayne]

Interesting symptoms. Its going in to limp mode which is why it won't change or kick down, but doing it at the change to 2nd gear is unusual.

The first thing to do is scan it for codes. Second thing to do is make sure the TCU isn't wet.

How does it behave in tiptronic? Put it straight in to tip from startup and without moving, then pull away and see what it does and whether it will change gears manually.

Its not the F125, and doesn't sound like a clutch drum as that usually manifests in 1st. I'm wondering whether its a solenoid fault, and that is very often caused by a wet TCU.