Hi Max,
Thank you for translating your response. I understand it is no easy, but using something like google translate works fine for me. I should be able to understand most of what you're saying. If you'd like to submit both the German and English like you did in the post above, that is ok.
What you experienced is called an MD5 Error. This is a bug that causes an area of the save to be reverted to the Day 1 state. I understand how frustrating and disappointing this error can be for players. For this error, there are multiple triggers that cause it. The team have already eradicated a large number of them, and are working to fix the remaining triggers.
As you are on XB1 there is a work around that players have found that helps them avoid MD5 errors that occur after a crash on the XB1 (another linked issue the team are working on). As this is a player found workaround, caution is advised -
https://7daystodie.com/forums/showthread.php?69218-Possible-work-around-and-or-solution-to-md5-crashes(base-wipes-resets)
For the crashes, a lot of players find that once they notice the indicators of a crash, hard resetting the console or clearing the cache by shutting down and unplugging for 5 mins, can help to avoid the crashes. Some of the indicators include - flickering menu screens, increase in severe weather and animals no longer spawning in the world.
Hopefully this translates back into German ok for you, if you have any further questions, please do not hesitate to post them here and I will get back to you asap. There is also no need to send a copy of your reply via Private Message to me, I check the forums before I check them.
Clare