Can't get vacuum to resume cleaning after recharging

Sorry the search function on this forum is horrible and I know this is probably answered somewhere, but…

Vacuum runs low on battery halfway through cleaning my 2000 sq ft office. Once it returns to the charger, it will charge to 100% and then just sit there. If I press the button on it to restart or press the button on my app, it starts from scratch rather than completing the remaining 50% of the floor. Is this a bug or am I doing something wrong?