Not sure there is too little information to determine an exact cause.  From
what you have said it sounds like someone else changed the table to a linked
table.  Perhaps they relocated it to create a central location for the file.
If anyone else has access to your database discuss with them this issue.

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And if you are a user and there is someone else that administrates this
database for the love of all that is good and holy please do not change
anything and discuss the issue with that person. You could do more harm than
good.
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