@Sankalp 

Hello, does this issue occur on some of the clients or all of them are behaving the same? What are the brands and models?

As per your description, it seems that when you are moving far from the A6, the 5G signal is not good enough, so the clients will choose the better 2.4G signal. However, when you are moving back, the 2.4G signal is still not bad and your clients choose to keep it but not switch to the 5G. You may try to disable the Smart Connect on the A6 to give it a go.

Good days.