Ever since the credit crash and implementation of Dodd/Frank bill rules, this has become more common. It almost seems that the lenders are not sure what they need when they start the process so after initial work, additional conditions are needed to be satisfied. I suppose that there are rankings of various parts of the application, which when not top notch, trigger additional information/data to overcome that deficiency. I just refinanced my home and it was almost continual requests for additional information that could have been provided at the outset, if they had asked for it.
Another common request for "additional information" is something like updated banking statements. If the process has been going on over the end of a month, the underwriter might ask for updated bank statements to ensure the funds are still there.
Talk to your lender and demand that they tell you EVERYTHING they need now, and anything they need in the future so you can get ahead of the info demand curve.
GRI, CRS, CLHMS, ABR e-Pro