Microsoft state that a small number of users said that after installing this update, the game’s performance was lower than expected.
Most users affected by this issue run the game in full screen or borderless mode, using two or more monitors. Microsoft said that it has resolved this issue and will use its known issue rollback function (KIR) to automatically undo this part of the patch to solve the problem.
The known issue rollback works by marking a specific patch as harmful and automatically returning to the old code path when the client checks the server. This feature is only used for non-security patches and may take a day to complete.