Hey, I just found an old post of yours from 2019, where you needed calendar help, but edited it since you figured it out. I am having this same issue, so I am really curious in how you figured it out since I can't seem to find a solution anywhere on the internet/any forums.
Like having winterfest in the summer and all that being a mess.
Except I am not using MCCC to make the days longer(i do have MCCC installed and use it for other things though). I do change the lenght of the seasons from 7 to 28 using the game settings.