Could be that there is a delay in sortiing out the first one. Usually any problems are encountered in the first draw down and then they are always sticky on the last one.
I just finished a house recently and know that my bank made a bit of a balls up of nearly every drawdown. The branch forgot to fax head office to draw down on one and I waited 1 month for funds, (went down like a lead balloon).
My advice is to draw down about 2 weeks before you need it and you should be ok