data merge not generating multiple records. Repeats one throughout

I’s doing a multiple record data merge in Indesign. I believe that I’ve set it up correctly and when I preview multiple record layout and preview each page I have all of 125 records viewing correctly however when I apply the merge, the merged file is generating the same data in every field? I have 280 names which preview fine and show the merged document will be 35 pages. The merged document is 35 pages but has the same name in every box and is not even the first record of my list? Can anyone shed any light on this. I’m doing 2 different merges from the same excel file and one is working fine while the other is not?