Out of Sequence Activities in Primavera P6

Out of Sequence activities are those which does not progresses according to the original schedule logic/sequence of the Baseline Program. As actual progress differs a lot from the Baseline sequence, which impacted the Network calculations, early dates for the future activities and thus true project completion date.
these activities are generated based on the scheduling techniques used to update the baseline program, there are three types of scheduling techniques in Primavera P6 software namely:
1. Retained Logic
2. Progress Override
3. Actual dates
Normally Client and Consultants recommended to use RETAIN LOGIC techniques for the updated program, in this technique the software taking into consideration of the Baseline logic and links to perform the network calculations to determine the future dates of the activity and its impact on project completion/if-any, whereas the PROGRESS OVERRIDE ignore these relationships in network calculations.
These OOS activities falsely shown the project completion (depending upon on particular situation) and determines the project completion which is not realistic therefore to reach a realistic project completion it is necessary to rectify these links while performing the periodic updates.
These OOS activities are considered as the "Schedule Error", and thus the Client/Consultant can reject the Contractor's claim based on the provided schedule and may instruct the Contractor to modify the schedule as per the actual site situation to reach a realistic project delay.