Are you opening this Excel document in Excel on your Mac?
Or are you opening an Excel file into Numbers?
If the former, your question should be asked in the Excel support community on the Microsoft website.
If the latter, opening your Excel file with Numbers converts that Excel document to a Numbers document.
In that Numbers document, a Table is an object placed on a Sheet, and moves with respect to the Sheet only if there is a user action that causes the Table to be moved to a different location on the sheet.
The Table may also be moved wrt its position on the screen if there is a user action that results in the Sheet being moved.
Both statements are true for other objects on the sheet: Images and Shapes can be moved on the Sheet, and will be moved on the screen if the Sheet containing those objects is moved.
ALL of these moves require a direct action of the user that moves the object or moves the sheet containing the object, or that changes the size or location of another object which the table is set to maintain distance from.
Missing from your description is any indication of what the user (you) is doing when the Table is moving. Become aware of the actions that are causing the move will move you closer to a solution.
Regards,
Barry