Append data from while-loop into columns

Good evening,

we use an Ocean Optics HR2000+ spectrometer to record continously spectras of our laser-system. For the spectrometer we use the plug-play drivers, located here

(http://sine.ni.com/apps/utf8/niid_web_display.download_page?p_id_guid=7833BD4A31DA1274E04400144FB7D21D).

The intention of our labview-program was to 

• Store in an well defined delay the spectras of the laser

The requirements to the stored file were

• First column: wavelength
• Appended columns: spectrum 
• Header of the column - elapsed time, after starting the program

After considering the forum, one of the solutions which was applied than was to use feedback nodes, together with transposing the data afterwards, as you can see in the attached files.

Our problem:

• for a short run of the vi it works fine
• for a longer run of the vi the file gets messed up (see testlong.txt): in the fifth instance of the loop the instance/wavelength got written again into the spreadsheed-file

Is there anything extremly stupid we have done here ?