Long time ago I wanted to trying to added a script of Dispatch or Add-ins with a condition - if the file already exists in Vault - to insert it only as shared.
For this purpose it is possible also to try to use in PDM context menu comand of Windows - MoveTo (if such comand is absent look as to add her).
I don't remember precisely for what reason, it was necessary to postpone the solution of this question (there was some problem).
Of course, it is important to allow to copy in what states as shared.
But it seemed to me it was a problem with control of the rights for UnCheking, Changing or Deleting (the right of the Author and other Users).
We have had this error few times as well. I have not ruled out user error yet totally. Since I have not been able to trigger this deliberately.
For us also the created times are not close to identical, so it does not seem to be a problem of traffic.
I've been thinking this might be linked to the fact that PDM returns unused numbers back for use. For example if user gets a number for save window but cancels the save or generates numbers for copy tree but does not go through with it.
Don´t know how crashes or network errors affect the serial number "returning". Our problems in the past have been mostly with users at a remote office with a ping of less than 80ms.
Most users are not aware that the numbers get reused, so they might think its possible to copy paste the numbers they left "unused".
We use unique file names -setting inside PDM, but since we use same part numbering for parts & assemblies, it is possible for us to have same part number as part and assembly. This can cause alot of issues when exporting to ERP system, since basically someone can accidentally override someone elses part with same named assembly.
We are using 2017 SP3@server and SP4.1 at clients. We have also very simple serial number adding generating the numbers.
In your screenshot, the first assembly has file extension as lowercase, and the later have the extension as capital letter. In my experience Solidworks saves file extension with capitals. But users can write the extension lower case. Do you think it could be possible first user was "reusing" a part number by typing filename manually and the second got a recycled serial number from the system? Edit: I just noticed you wrote that the first user did not manually renamed, that makes this more intresting for sure . I'll try to remember report back my next problem with the serial number when we have one.
I think your issue is reported in SPR 769689 which was fixed in 2016. This is a problem with assemblies that produce reference dialogs when doing a save as and the user hitting cancel on those causing the serial number to end up getting pushed back to the top of the stack to be used again.