Would like to offer a possible solution for this after facing the issue myself (had updated about facing this issue on a similar thread which I am unable to find now)
My exam was stuck right when I started IR and I got the error message with code ES007(software attempting to show wrong question) in addition to being stuck at "Please wait". Try out the following steps:
1. Delete cookies/cache + ALL browsing history.
2. If neither works- call the US helpline available on their website for gmatprep products. You may have to try multiple times to get through as their lines are mostly busy but keep trying and let them know, mailing them would be very slow and did not quite work for me. After I called them they were able to resolve it within a day.
PS
1) Make sure to delete ALL browsing history. Even after I was told by email that my issue was resolved, simply re-logging after deleting cookies/cache did not work. It worked only after I deleted all browsing history.
2) I was told that this error props up when you have(or have had) multiple tabs opened for their website/multiple browsers, even though this was not the case for me. So its probably a good idea to delete all the history etc before starting with the mock.
3) I was using an attached monitor to give the mock, don't really know if that was a point of concern but was able to load the test page after issue was resolved once I disconnected the monitor.
Hope this helps!