This is a very specific issue. The cheaply made low quality charging and balance controllers being used are the cause. Sadly some of the bigger companies are using cheap as chips inferior quality controllers from China as a cost saving measure, so buying a big name electric toy doesn't guarantee quality.
In the EU CE ratings need to be enforced more strictly and in the US Consumer Protection Agency needs to gain punitive authority so they crack down on the trash tier quality many companies are selling.
One need only search Amazon for DC voltage controller to find all manner of electronic firestarters....