The row number and WBS Sort columns show a different number in the Timeline and Grid views.
The Timeline is showing the row number in the "WBS column", which is not necessarily the same as the "WBS Sort" number.
If you create 3 tasks, you will see the following:
In this scenario, "WBS" and "WBS Sort" are the same.
However, if you delete one task, such as Task1 or Task2, the row number is updated (these are all consecutive), but the WBS Sort order is not recalculated. The reason is that there are several columns using this to keep the order and structure in the tasks hierarchy (such as level, parent, next task, ...), and they have many relationships between them.
Deleting Task1 would leave us with the following:
WBS Sort number will be kept, but WBS Row (a different attribute, as you can see) shows the tasks in the same order as the WBS sort, but sequentially. There are certain scenarios where the WBS Sort could change, but this attribute is not guaranteed to be sequential.
Release : Any
This by design as WBS/Row and WBS Sort are two different columns.
The WBS/Row column is a dynamically generated number only available from the Task Timeline. It provides the user with a reference to the task timeline hierarchical rows in the format of a WBS number or a Row number. This value is not stored in the database. The values displayed can change based on filtering.
The WBS Sort column is a sequential number that may have gaps in the actual numbers stored in the Task table in the database. This is the field that is used to physically sort the tasks in a simple WBS order. The numbering may change when Tasks are moved up and down the hierarchy. The numbering may have gaps due to the deletion of tasks because the entire WBS Sort numbers are not recomputed when a task is deleted.