That unit was wholesaled by Honda back on 4/10/12, but was never registered by the original retail buyer.
If you are the original buyer, you can still register the mower and have the 5-year warranty clock start on the date you can provide proof-of purchase. If you don't have proof-of-purchase, the 5-year warranty clock would start on 4/10/12. Either way, and even if you are not the original owner,
the mower is still under factory warranty. So, I'd suggest you take it to a servicing Honda dealer and have it inspected and evaluated. If there are factory defects found, cost to repair them are usually covered under warranty. Be sure you communicate with the Honda dealer what is or isn't going to be paid for before the work is authorized.
Use this link and enter your ZIP code to find a dealer in your area:
Find A Honda Dealer
I understand it may not always be easy to get the mower to a dealer, but to obtain warranty service, it's the only choice. You can try and DIY repairs, but you'd still need to have contact with a dealer to get any parts needed, and that can get costly. For example, a replacement transmission is $139.73. On the other hand, it could be a simple cable adjustment or debris interfering with the controls/linkage. I'd suspect something in the left side axle gear, bushing, etc. is the problem, but that's just a guess.