Second gear failure (pops out under load)
These gearboxes are infamous for popping out of second gear under hard acceleration once the engagement dogs round off — there are NHTSA complaints and two decades of forum threads on it. On the test ride, load second gear hard from low rpm and feel for it jumping into a false neutral. A real fix means splitting the cases for new or undercut gears, so price the bike accordingly.
Ask for repair records covering this item. If it hasn't been addressed and the car is in or near the mileage window, price the $1,000–$1,800 repair into your offer — or make it the seller's problem.