More than likely you have raw fuel in the EVAP canister. When this happens it breaks down the charcoal and it will cause the purge valve to stick.
If it were me, I would replace the canisters and the purge valve and then retest it. However, if this happens only after filling the tank this is almost guaranteed to be the issue. I would be very surprised if you don't find the purge valve stuck and hear raw fuel in the canisters when you shake them. This system is only meant to have fuel vapor in it to reduce emissions and improve fuel mileage.
Please let me know what you find. Thanks
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Tuesday, October 22nd, 2019 AT 7:22 PM