@JuergenB84
I now suspect your problem could be combination of many issues RAM memory,OS patch status and disk space because I see your host machine has only 12 GB physical memory allocated while Cloudera recommends not less than 8 GB but 12 GB is optimum to operate the Sandbox and in comparision to my sandbox is at 40 without running anny sqoop job etc
Your guest machine has other applications which reserver memory on startup literally sharing the same memory spacee for your system starving your OS the VM disk vdi has an elastic value personally the machine I compared with yours runs no jobs buit already comsuming almost 40 GB !!
This link could help you learning-ropes