I'm also thinking mirror up mode, or perhaps possibly timer mode, which would delay both the shutter opening and closing but might be mistaken for a long shutter period. make sure the dial on the left side is set to S for single exposure then repeat the test. you might want to try a full camera reset then remove the battery, power switch on, and depress the shutter button for a few seconds to remove any stray voltage in camera, reinsert the battery and see how it performs.
Not having a sample image makes it tough to really diagnose issues be it a camera problem or just operator error. If possible use your own memory card so you can later upload an image complete with exif data.
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