Paving not even and firm - what helps?

Ok, so that means, remove all the crooked parts, fill under again with split, and then shake. That’s annoying.

Yes, it probably won't work any other way. If there is enough loose gravel under the stones, you will eventually get them fixed, but it will become increasingly uneven.

How heavy was the vibrating plate?
But normally it looks more crooked before vibrating than afterwards, not the other way around...

Have now spoken with a neighbor who is a former road builder. He said the small vibrating plate was a toy and he had already wondered while watching. Next week a 200kg machine is coming, which is supposed to smooth out the situation. The stones that have sunken will be taken out again and reset, and then the whole thing will be repeated as many times as necessary until it fits. Let's hope for the best.

Depends on how much uncompacted gravel and sand are underneath. Make sure the 200 kg slab has more Kn than the small one and approximately the same support area. Weight isn't everything.

Below is gravel, which is very hard, then they took more gravel to level it out and then a little sand so that the stone lies flat.

The sand disappears into the air inlets of the gravel layer... it disappears so to speak, and uncontrollably.