The '9' in the model name means it is a K9 (version code) model, which has a slip-belt design transmission. The belt should be a bit loose, and when you operate the SmartDrive control, you are rotating the transmission, which causes the belt to tighten around the engine's pulley and in the input pulley on the transmission. Have a helper fully engage the SmartDrive control and the belt should be snug. If it is still loose, then the cable can be adjusted.
Related, Honda did issue a Service Bulletin back in April of 2015 where the belt would come off the engine pulley, often due to light debris (sticks, pine cones, etc.). Honda redesigned the pulley and belt guide to resolve the problem. The updated pulley has a deeper groove, so the belt rides deeper, and the belt guard shape was revised as well.
The updated pulley and guard were applied to production model HRR2169VKA models starting with serial number MZCG-9370838.
Drop me a private message with your email, and I'll send you a copy of the bulletin; it's got nice photos and procedure on how to get to the belt. Include the serial number of your mower, and I can check on its warranty status. It came with a 3-year warranty, BTW, and if still active, and a dealer determines your mower has this issue, repairs would be covered under warranty.