Getting error in production, not in dev or QA - Could not load file or assembly 'DocumentFormat.OpenXml, Version=2.7.2.0

Have an web application that calls a WebService backend. Everything was worked as expected. Not sure exactly when it started but now in production we are getting this error:

2019-10-22 14:27:05,841 [193] ERROR VplApiService.Controllers.BillingController - Uh oh, something happened!. We are unable to process this LTL Invoice file from file VantagePointShipmentDetailReport.xlsx System.IO.FileLoadException: Could not load file or assembly 'DocumentFormat.OpenXml, Version=2.7.2.0, Culture=neutral, PublicKeyToken=8fb06cb64d019a17' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040) File name: 'DocumentFormat.OpenXml, Version=2.7.2.0, Culture=neutral, PublicKeyToken=8fb06cb64d019a17' at VPLServices.Shipments.ShipmentService.ProcessEDISupplementalData(String fileName, Byte[] fileData) at VplApiService.Controllers.ShipmentsController.d__18.MoveNext()

Running the code base locally, I am not getting the error, everything is working well.

Pointing to our QA environment, I am also not getting the error, even though I just re-deployed the exact same code as what is in production.

My suspicion is that someone manually messed with a DLL or something on prod. But, how can I tell what DLL? And, more importantly, how can I fix this?

Thank You, Sammer