Time elapsed equal to 00:00:00

Time elapsed equal to 00:00:00

I've analysed the reports of last month in more details and I saw that for some tickets the 'time elapsed' is '00:00:00' with the 'request status' on 'closed'.
The 'time created' is 'May 4, 2018 08:35 AM' and the 'close time' is 'May 4, 2018 10:32 AM' .

Any one an explanation or a direction where I should go to analyse this.

For the same month, we 've tickets were the 'time elapsed' is correctly calculated.

regards
Koen Vlemincx

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