Inputs and "next" keyboard button: two hits necessary

when having several inputs (text, number, the behavior is the same) and using the “next” button on the keyboard, I noticed the following behavior : it requires hitting the button twice to go from the first input the focus is in, to the next one. After this initial two hits, only one hit is necessary to keep moving from one input to the next. The same problem arises even if the tabindex is defined in the inputs.

I have seen this behavior on Android device (not tested on iOS), and you can even reproduce this using the Chrome “device mode” and using the tab key. Here is a simple codepen with 4 inputs :

Anyone knows why ?