I have had more than one conversation with someone cohabiting in a nominal second marriage with an apparently valid previous marriage unresolved. I have assisted more than one with processes of having the validity of their marriage considered.

I have observed none of them in that situation present at the rail for Communion. My Catholic friends and relatives do understand the Church's teaching and discipline and don't hold themselves above it.

If they do such a thing based on some rationale or other, I would hope they would do so where they are unknown in order not to compound their error with scandal.