Cannot update existing query studio report

[vovanenok]

Hi all!
User cannot update existing query studio report:
1). user can open existing query studio report, but cannot save it, the error message appears:
severity : error
errorCode : LoadBalanceHandler.unknownServerGroup

2). user can create a new query studio report and save it, but when try to press "Save" button again, the error message appears:
severity : error
errorCode : LoadBalanceHandler.unknownServerGroup

At the same time, user successfully can "Save as" opened query studio
report with another name.
Please suggest any idea ASAP.
thanks in advance