Update.
I met the situation again yesterday, luckily or not. This time is the issue I met but I didn’t mention last time in the article.
Another situation is sometimes, the variables which display on the screen are disappear.
But if you click the button into Expression Editor, sometimes it still show the variable what you assigned, or it might change the variable to the other ones.
Here’s the picture
On the picture, you can see no only just one activity, another “Multiple assign” on the left side also has the same issue.
[Update 2020/03/12]
Another one.
You can see the content display on the right side of the assign Activity(“%”), is different to the content from Properties(“”).