@All: Thanks for your Responses and ideas for possible causes.
The interesting Point ist that the Problem only occurs on fruits of variety "Mango", fruits of other Paw Paws varieties are not affected. this could mean that under certain circumstances "mango" is particularly susceptible to ripping open the fruit.
This year was extremely dry, and I watered the mango a little. The tree stands (like the other trees) in sandy soil that dries out relatively quickly. The ripping of the fruit began more when it became autumnal, the nights cooler, and even more when rain started. Perhaps the weather conditions had an influence here. In fact, there are many pests imported with fruit or other goods such as plants, such as the cherry vinegar fly (Drosophila suzukii ) or the boxwood borer (Glyphodes perspectalis), whether or not moths that go on Paw Paws live here, I don't know. When opening the torn fruits I couldn't find any maggot or maggot fodder, nor any excrements.
It also doesn't look like a fungus is the cause, at least there are no visible fruiting bodies on freshly torn fruits, of course the flesh starts to rot or get moldy a few days later, but I would say this is more of a consequence than not the cause of the crack.
I will continue to observe this in the next few years, to what extent other PawPaw varieties or even Cherimoya one day have fruit bursts, or whether this effect is still limited to mango only, or whether it was just a consequence of the weather in this year and will not occur again in the next few years.