Based on comments and my own testing this issue appears to be caused by players updating their servers by only copying the executable (bedrock_server) from the 1.16 download into an existing BDS installation, or using a Docker container/game panel with the same issue. The executable and all supporting files it is provided with need to be upgraded for BDS to function properly, it does not act in the same way as Java.

To resolve:

1. Extract the new 1.16 BDS files
2. Copy the worlds folder, server.properties, whitelist.json and permissions.json from the old folder into the new one
3. Run BDS

If you believe you are experiencing the issue and your BDS files have been updated properly please provide more information, including a download of your world and BDS files in the comments.