I didn't do anything different, but it seems to be working today (04/15). I was able to catch up on all the dates in the calendar and they are being saved as completed.
Update, 04/16/24 02:56: I just finished playing today's challenges & found out that the challenges for 04/15 were not saved from yesterday even though I completed them yesterday.
========== update as of May 20, 2024 ==============
So far, the games have been saving correctly each day for about a week now. All of my May games are up to date.
========== update as of May 25, 2024 ==============
The games are still saving correctly. Maybe the issue has been fixed.