I've faced the exact same issue yesterday. Though my status was still "In Progress" as they had received my documents on 28th May. Now yesterday, they've changed the status to "On Hold" and sent me an email as well stating "This is to advise you that photocopies of your documents have been sent to Indian Institute of Management, Kolkata for verification and that your file has been placed on hold until we receive their written response."

I just talked to the concerned person at my institute and he said he hasn't received anything yet. I now feel WES is doing this as a deliberate ploy to delay the process! Any seniors here who have faced the same issue earlier and can tell how much time does it typically take to resolve this?
Also, have any of you who called got to know any specific reason for this additional verification? I'll try to call them when they open office today.