@Nabil , I’m not sure about your issue but this seems exactly the same what I was seeing in one of my dives, Suunto confirmed an update is required to solve this. But to be sure, report this to support@suunto.com. Then, please read the “Mandatory Gas Time Alarm at beginning of the dive” thread carefully, I had the same on a dive where Tank Pressure was - - <null>.
If you download the json file of your dive you can analyze as described. Read:
https://forum.suunto.com/post/194823,
https://forum.suunto.com/post/194868,
https://forum.suunto.com/post/194881, https://forum.suunto.com/post/194890.