Congratulation and thank you for the fix :-)

@robro , your files removed. What was the problem? can you share your experience?

@QtExchange said in Segmentation fault or overflow when streaming from a QSerialPort:

The trick is one QByteArray receives the data (on signal slot basis)

QByteArray can receive nothing, it's an array of bytes - a container, nothing more, nothing less.

where the other container (which is just a copy of the receiver-QByteArray) is parsing the received Data, as the symbols come in a random order.

??!
How can you parse something that doesn't have any order? And where is this other container?

I could think of having an extra signal-slot that exchanges the data between both containers whenever it is demanded, but it sounds like I have to double check if I'm actually dealing with the most current data.

I don't follow. Why would be this even needed ...?

There's an extra mutex for the device access, and another one for the shared message container.

Qt imposes thread affinity on QObject instances, you don't need a mutex for device access, and you shouldn't share the message container.

and because I'm dealing with QElapsedTimer, that needs the thread.

In what universe QElapsedTimer needs a thread ...?! It's like saying that an integer needs a thread ... I don't get it.

I am sorry about my last post. I made a stupid error. I updatet to QT5.5, but I haven't reconfigurated the project, so I was still using QT5.4.
Now I tried also the Chipi-X10 USB-RS converters. I have to say, they work a lot better. I have now for all three ports, this converter. With the others, a lot of times I had to unplug and replug the connectors to get dem work. So there is something strange. The Chipi worked really good until now, thank you jeroen3, this will save a lot of time.
After building the programm with QT5.5, the programm also work a lot better. I saw that the qcustemplot keeps plotting while I drag and drop the window. I have sometimes errors but now only sporadic. For example when I resize the window very fast, I can provoke it. But in general the errorrate is about one or two percent, and with that I can live.

PS: We here do not play in telepathists and predictors. If you want to get help, you should provide the minimal and simple example....

My problem was, that with the minimal simple example all seems to working. This communication problem I had only, wenn all the data was coming and when I was plotting someting in the same time. And I checked my code a lot of times. The problem is, my knowhow about QT and generell about programming with PCs is not very big. So I think there is something I do not know. So when I check my code a hundet times more, I will not find an error.

I made also an easy experiment to isolate the error:
My I slowed up the replot, so that I plot only every tenth time, but ten points at the same time. Like this I can see, that this error, comes only when the window is plotting. The error comes more, the more points he has to plot on the screen. So if I make fullscreen, and I set up the scale so that I have the maximum of points in the axis, the error comes every time again.
So QT has an influence to this problem. I think there is an overflow in some buffer, beause the program is to slow to read it or that he overwrites any part for some other reasons. But anyway.. For me I will pay attention now to not overcharge my comuter :)
Thank you for all help!