Hi Eric and Wolfgang,
after installation of a swap file, I was successful in compiling Kstars and Ekos from source. Now I have Version 3.4.3 (before it showed 3.4.2). With this I don`t encounter the crashes as I did before. So, Thank you both for helping!
I will do some more testing and if I encounter strange behaviour again, I will tell you. As for now, this thread can be closed.
Thanks and have a great day.