I wrote an application years ago that loaded data from spreadsheets, stored it in a database, mashed it around a bit and then produced reports. It took around 5 minutes to complete the process for a spreadsheet and this was acceptable (those were the days). Then the department that used it moved from London - where the database server was - to Glasgow and the processing time ballooned to 45+ minutes and sometimes just hung indefinitely. We had weeks of back and forth between DBAs, Devs and network people. The application hadn't changed, the database hadn't changed, the network wasn't maxing out at any point. The only change was the location of the users. It turned out that the application was too chatty with the database; for each row in the spreadsheet, it was doing lookups to the database to enrich the data - opening and closing a connection each time. When the users were in the same building as the server, the connection latency was just about acceptable, but over a wider network it was a major problem.
My point is; just because one element hasn't changed, it doesn't mean that it isn't the cause of the problem.