It sounds like magazine latch/shell release issue(s), either sticking (crud underneath) or an errant spring for it.- but a bent part is also a possibility.
Also, if it was used a lot, it could be that a soft latch tip has worn or chipped, allowing the second shell to pass out of the magazine tube.
I would diagnose it, loading only two shell into the magazine, then observing the latch operation (or non-operation, as the case may be) while the slide is operated slowly to feed the shells out of the mag.
For safety, if the BBL's easily removable, the mag can be tested with the barrel out of the receiver.
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