Adding items to a public List of class is not working.

[Erenyx]

1. When I have a button to add bunches of items simultaneously to a public list, the list is extended will class of Null but not exactly what I am trying to add. I have to click the button again and again so that the Null would be replaced by the actual item. Also, it is added pages by pages when the list is folded. In version 2.1.10
2. Here is the way to reproduce it:‌

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After I click the button. This is what I get.

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Because I have 42 items, so after I click 42 times, this is what I get, but this is what I expect to have after one click:

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4. Unity 2019.3.3f1

5. 2.1.10

6. No

7. Mac