The analyzer detected a possible error that has to do with using method 'OrderBy' or 'OrderByDescending' for a collection of type 'IOrderedEnumerable'. It may be related to the fact that this method was called twice while the second call should actually have been done to method 'ThenBy' or 'ThenByDescending'. The problem about this issue is that calling 'OrderBy...' for the second time won't take into account the first sort order of the collection, unlike 'ThenBy...'.
Consider the following example:
var seq = points.OrderBy(item => item.Line) .OrderBy(item => item.Column);
In this code, a sequence is first sorted by lines, and then the resulting collection is re-sorted by columns. The second sort ignores the result of the first sort.
To keep the previous sort result, one must call the 'ThenBy' method for the second sort.
var seq = points.OrderBy(item => item.Line) .ThenBy(item => item.Column);
A similar mistake can be made when using query syntax:
var seq = from item in points orderby item.Line orderby item.Column select item;
The second sort will lead to losing the first result, too. The code can be fixed as follows:
var seq = from item in points orderby item.Line, item.Column select item;