Issues with a Sprint START and END date

[Dmitriy Yerebakan]

I have created a sprint with the fixed START and END date but after I save the dates Jira changes the dates and if I will edit the dates again, Jira will set the different dates again. 

[Andy Heinzer]

Are the dates showing in Jira off by exactly 1 day from the dates that you entered?

If so, then I suspect that the problem here is that your user profile is using a timezone that is different from the timezone that the Jira application is using.  And that you are likely 1 or more hours ahead of the Jira system timezone.  

Many times when a field is Jira is asking only for a date, it's actually trying to store that date value with a complete date/time field on the backend.  In turn it tends to pick that time as 00:00.  So what I think is happening is that you enter a date such as 5 October 2018.  But when that date is saved in the system, it's taking into account your advanced timezone and in turn saves that as 4 October 2018, 23:00 if you were one hour ahead.

I found a related thread to this in https://community.atlassian.com/t5/Jira-questions/How-do-you-set-a-default-time-zone-for-a-Jira-Cloud-instance/qaq-p/632137

As for how to go about dealing with this depends on a number of factors.   If all your other users are using the same timezone, it might help to set your preferred timezone in your user profile to use the same as your colleagues, or the Jira System is using.

[Dmitriy Yerebakan]

Will check this assumption, thank you! 

But usually system change the date on months, for example usually I have such case: 

1. I have created a Sprint (09/24 - 09/28) but System sets the following dates (06/05 - 09/28)
2. When I'm trying to update the START date system can change the end date on week or months earlier. The same will be if I will change the END date.