I’ve identified the cause: the game screen is being cut off, which seems to be misaligning the hitboxes for certain system elements.
Furthermore, the gameplay itself suffers from a lack of explanation in almost every regard. For instance, there is no clear way to buy items (there is no "buy" button), the conditions for triggering a "Game Over" upon defeat in battle are inconsistent and unclear, and training suddenly becomes unavailable even when there is plenty of stamina remaining.
The game balance is also quite poor; enemies that can instantly kill the player with a single hit appear abruptly—making it impossible to bring back treasure chest loot since encounters are guaranteed to happen frequently—and losing a battle results in the total loss of all collected items. These issues combine to make the prospect of going on an adventure completely unappealing.