@NAViLERA interesting problem, friend!
Is it possible this is a bug? You could try reporting that UI issue from the Samsung Members app by sending over a error log.
This is a really valuable feature, in that it will extend the life of your battery for years. But it is a bit buggy in terms of switching it on or off. I reckon the designers have not really taken into account the fact that users might want to turn it on and off*.
My advice is to check the voltage of your battery - that will give you an unambiguous indication of whether the S5e is charged to a high voltage (100%), or a reasonable voltage (85%), irrespective of whether the tablet reports it as 100% or 85%.
Many apps will report your battery's voltage. I use "AccuBattery" by "Digibites", which is a realiable and well-regarded app. But beware - whilst AccuBattery will report the battery's voltage correctly, it too will become confused - although not about voltage - if you switch between "protect battery" enabled and disabled.
*Enabling and disabling "protect battery" is a smart thing to do. I have protect battery enabled permanently, unless I am travelling and really need the full 100% capacity of my battery to get me through a trip, which is rare. If you don't need the full 100%, then setting "protect battery" will extend the battery life (in years) of your tablet massively