I am using the latest version of Harvest Festival Legacy (0.6.8) and Forge (14.23.5.2847). The calendar overlay is not displaying when Pixelmon (reforged version 7.1.0-0.3.2 and Generations version 2.9.1) is installed.

Here are the download links to the respective Pixelmon versions:

http://adfoc.us/24937872744102 - Reforged

https://www.mediafire.com/file/equbniqbl1gykl4/PixelmonGenerations-1.12.2-2.9.1-universal.jar/file