PPPoE Disconnections

My network setup is as follows:

ISP RB411 RB912 SXT 5 RB912 SXT Lite 5 TP Link Router (PPPoE)

I notice on my customers page lots of disconnections on my account.
Despite that, the internet works normal every time I use it.
But, I have many customers who are facing those disconnections.
How may I identify the reasons behind this and get rid of them?
I may provide with any more necessary details if needed.

Thank you

what is this ??!!
you have to check all of them separately…

I already did man and compared 2 clients ping from their SXT to my main sector and got the same results wheres one of them has no disconnections at all and the other keeps disconnecting.