Actually that’s saying UTC +3 and UTC+4.
MSK = UTC+3
British Summer Time (BST) = UTC +1
Greenwich Mean Time ~= UTC
So when the UK moves from BST to GMT in a few days, they will move from UTC+1 to UTC.
But it also shows that your server is running in UTC+4 timezone, so when you display times in MSK, it will be displayed as Time-1h due to the Timezones…
For further troubleshooting, could you try setting the dueDate with an explicit timezone?