Highchart x-axis shows label shows randomly

i'm dealing with a strange Highcharts error that's kind of random.

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facts:

• i'm making a weather chart with highcharts


• the chain is: javascript highcharts -> converts to svg -> converts to png -> use mpdf to generate multiple page pdf with different charts


• the data comes from an external xml, and its parsed with php

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problem:

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  sometimes x-axis label shows date (day number + day label, ex: "10-Feb")

  
  


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  example of random error in label: http://ift.tt/1Bxuwn1

  
  

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Anyone knows why this may happen?

Thanks!

(if you'd like i can post the code)