Tasks not appearing for some users within one group

Hi All,

I have this particular issue where users handles a task steps back and when the user go back to the report he can no longer see the task. I first thought this is security issue but then he told me his colleague who has same groups as him can see this task. I am wondering what could go wrong it started after we released application to the production, but it affects all of the applications that are not related to the one we released. Any suggestions what to check/do ?

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