Lime Survey version: 6.8.1
Own server
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We have exported a .lss file from an older version of Lime Survey (3.22.6) to a new version (6.8.1) that is running with different encryption keys.
The survey is imported successfully, can be activated, and users can add responses. However, submitting the survey fails due to the different encryption keys.
We are unable to re-use the old encryption keys, and we are not copying any responses between the two instances, only the survey structure.

How can we move a survey structure to a new lime survey instance?
 

There are no encryption system in LSS file.

There are no reason encryption key broke with an LSS file.
I think you have the same issue with a new survey just created.

Maybe you have 2 different encryption key  one in config.php and one in security.php ?