I've been receiving an error since 9.01..."HandyNotes_Achievements\Libs/InSeason-1.1/InSeason-1.1.lua22; attempt to call field 'GetDate' (a nil value)"

Fixed in 3ca1800.

You can help us by testing by using a build from automatic builds, and reporting back results. Alternatively, you could wait for a release via CurseForge.