Hi,
Please check snap and glue settings, ensure that the Snap and Glue settings are properly configured. Go to View > Visual Aids and make sure that both Snap and Glue are enabled.
Sometimes, adjusting the snap strength can help. You can do this by going to File > Options > Advanced and then scrolling down to the Editing Options section. Here, you can adjust the snap strength to see if it improves the snapping behavior.
If the file itself might be corrupted, try copying the tables and relationships to a new Visio document and see if the issue persists.
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