After you install the January 2019 Cumulative Update for Microsoft Skype for Business Server 2015, the UCWA clients (Skype for Business on Mac and Skype for Business for iOS) show the "Rate my Call" window randomly after a user ends a call. This scenario isn't expected because the value for the RateMyCallDisplayPercentage setting is set to 0 and the RateMyCallAllowCustomUserFeedback parameter is set to False in client policies.
This issue also occurs in Skype for Business Server 2019.