The behavior you describe is a work in progress.
In Survey123 version 1.1, for a required field that has a relevant expression applied, the required field should be enforced if the question is relevant, and not enforced if the question is not relevant.
In the pending Survey123 version 1.4, this will be extended to where the relevant expression is applied to a group (ie: currently it wont work if the expression is applied to a group).