I have found that nodes used to manipulate arrays can not display comments (GET, REMOVE, FIND, ADD,…).
[Bug] Can't use Comment on Array Functions (GET, etc)
Thanks for your report! This is a known issue reported here:
We have a bug report in our system for it (UE-11414). I will post here when I see any update on it.
It looks like this bug has been fixed for 4.8, and you should see it in the next release. Thanks again!