A customer reported that the date vanished from their taskbar, but it was there yesterday. They included a screen shot, which showed a vertically-docked taskbar on a Chinese system, and the clock showed simply "10:50". The customer sent the message on October 10.
I used my psychic powers to debug the problem. Maybe you can too.
The problem is that the date is October 10, or "10月10日". Yesterday was "10月9日". What's so special about "10月10日" compared to "10月9日"?
It's one character longer.
The user resized their taskbar so that there was room to show "10月9日", but not enough room to show "10月10日".
The customer experimented by changing the date, and they confirmed that the date vanishes whenever you are in October, November, or December, and the day of the month is 10 or higher.