Hi Andreas,
There are several reasons that cause the file is locked, you could refer to this: "The document is locked for editing by another user" error message when you try to open a document in Word.
1, Word previously quit improperly and, therefore, did not delete the owner file.
2, A second instance of Word is running in the background with the document already open.
3, The document is shared over a network, and another user has it open.
To make this better: delete the temporary folders or files here are few ways to do that:
1, quite the client completely when you close Office.
2, manually delete the temporary files and folders:
In Terminal, paste the following: defaults write com.apple.finder AppleShowAllFiles YES
Press return
Hold ‘alt’ on your keyboard, then right click on the Finder icon in the dock and click Relaunch.
In finder, go to the folder where the problem doc exists.
Delete: .~lock.(Doc Name).ods#(or ~lock.xxx.ods# )
Regards,
Alex