There will be some differences like this in the EV values for preflop all-ins. PT3 needs to calculate the EV very fast, and therefore can only run a limited number of possibilities based on the known cards. Postflop this will be pretty accurate as the number of possible outcomes is manageable, but preflop there are a lot more possibilities. If you refresh the report you will see a different value, within a range of the right value.
When the mechanism is changed to calculate EV at import time and store it in the database it will be made more accurate.