Cart Confirmation could not be loaded

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PERMISSION_VIOLATION

Some customers that repeatedly use guest checkout will spontaneously switch their session to another customer record. For example, a customer with email test@test.com and internal id 15611 will submit SO12345. Then, the cart confirmation will try to load SO12345 and throw the error. I track the error message back to a different customer internal id 13423 that has the same email address test@test.com. Has anyone else run into this?