The date of Tuen Ng Festival in Hong Kong is wrong in korganizer. The calendar shows 7 May 2019, however, according to the gov't website, it should be 7 June 2019. The authoritative source can be found below. https://www.gov.hk/en/about/abouthk/holiday/2019.htm
Is there any algorithm behind those dates? You may want to have a look at the source file, there are the holidays until 2030. There may be more mistakes: https://cgit.kde.org/kholidays.git/tree/holidays/plan2/holiday_hk_en-gb https://cgit.kde.org/kholidays.git/tree/holidays/plan2/holiday_hk_zh-cn Maybe you update the files and attach them here, than we can create a patch.
Git commit eb1d23a58f903e06651fb2f461926c01c76934a1 by Allen Winter. Committed on 15/09/2018 at 14:16. Pushed by winterz into branch 'master'. holiday_hk_* - fix date for Tuen Ng Festival in 2019 FIXED-IN: 5.51.0 M +1 -1 holidays/plan2/holiday_hk_en-gb M +1 -1 holidays/plan2/holiday_hk_zh-cn https://commits.kde.org/kholidays/eb1d23a58f903e06651fb2f461926c01c76934a1