What causes the container to swell? Is the product defective?

Soy sauce and glucose syrup are fermented products. To protect nutrients, sterilization is not performed; instead, pasteurization is used.
The beneficial microorganisms that remain can produce carbon dioxide (CO2) due to exposure to the surrounding environment and air, which may cause the containers to swell.

However, there is no nutrient degradation, and it is completely safe for consumption.

* Pasteurization: Kills only harmful bacteria / Sterilization: Kills all bacteria, including beneficial ones