This seems to be the same problem that we found with Relevanssi Premium and ACF Pro (v5) a few months back – now showing itself with ACF version 4.4.1
The Relevanssi developer replied then see
https://wordpress.org/support/topic/backend-search-and-advanced-custom-fields-v5-not-working
which recommends some code to be added to functions.php
I have just tried that and it works for this latest version of ACF 4 too (i.e. using Relevanssi on the backend admin does not interfere with ACF listing relational fields).
