99% open rate - can't be true

I wonder if anyone else has encountered this: We've had a handful of seemingly random emails reach 97-99% open rate when our usual is 20-30%. The support team at Constant Contact believes that a bot is responsible for opening the emails. Our IT/cybersecurity team says if that were the case, wouldn't it be 100% open rate? Researching our cybersecurity tools shows no obvious answer. Do you ever see an email with an exceptionally high open rate, one you believe to be wrong? What was to blame? Thanks for any ideas or guidance.