I think the subject of your question is different than what you are asking for. To find who deleted the records you can refer to the below article that specifies how to find who deleted a record through the Recycle Bin or the Dataloader
In terms of finding how they were deleted I would suggest using the debug logs and specifying the user as the Trace Entity Name. You can then see what triggers/automation is causing the deletion.
Sometimes with managed packages the actual function of how the record is deleted is hidden but you will be able to see that a record entered a managed package and then determine if it was deleted or not.
I would also recommend reaching out to ServiceMax and explaining the issue and see if they have the ability to review what is going on from their end.