Why no ajax update???

Hello
Why if I stay on one product I cannot see any change of the progress bar?
For example, I purchased the black t-shirt of one size and want to add another t-shirt of the same product but bigger size- I see no change in the status!

Please see the video:
https://www.screenpresso.com/=3rukb

If no change in the status of a progress bar on the product page – your plugin is useless.

Thanks.