Hello from my point of view the problem is not in list append
please check the source of the list in UI and the rows parameter in the UI
some time its happened we give source as data action and in the expression of row we are passing local current data or vice versa (same source list and same current record for that list in expression better understanding pasting below Screenshot)
make sure that your source and expression coming from one thing only (i.e list of local variable and expression for current record also )
and from the first look its looking that issue only