I can type in ??? directly with copy and paste to EJS as property value.
And the compiled file also work fine.

For your case, it might due to character code which is not implemented in your local language code.
It might be solved by using  native2ascii  to conver your local language code to utf-8

For me: the language code is big5
I type in ??? into test.txt and I use the following to convert it into utf-8 code:

native2ascii -encoding big5 test.txt test_utf8.txt

And the result in test_utf8.txt is

And I put the above code into property field for label, it also shown as "???" in EJS working window.
However, it is not working with compiled simulation.

I think the problem is related to local language issue (with java). You need to ask help from local java programmer in your country.