To allow PeerSync to keep retrying open and inaccessible files to increase the chance for a locked file to be replicated to the target successfully, you can include 0 in the Maximum number of retries:
Change the drop-down list in the top left from Basic to Advanced.
Select File Options -> Open Files -> Global Settings (bottom of pane).
In the window below, check the first option to Retry Open/inaccessible files every x seconds.
Enter the range of time you want PeerSync to keep retrying inaccessible files.
Set the maximum number of retries to be 0.
Keep in mind this could be resource intensive (stored in memory) and concurrent file events may be queued until the inaccessible file has been replicated).