Are you sure it’s not because of time zone changes that this is occurring ?? I know it’s not helpful that we can’t tell Where our server has its time zone set to but … it sounds like the time zone the server is set at has had a time change to due to start or finish of the daylight saving / summertime and you have not…or vice verse?
(Eg in a different game I raid with a group based in Germany, but I am in Australia. Their time has changed but mine hasn’t yet … so for this week it will be one hour earlier than it has been over summer for me. And then after my daylight savings time finishes it will be two hours early than it has been for the last few months.)
I also suggest that you try reporting the server by the report official server tool with the problem as being raid time window is x to x in x time zone which is different from x-date … check if server is set correctly.