Translating complex, politicised and ambiguous European legislation and case law into practice is the difficult everyday condition for street-level bureaucrats in European Member States. Yet their crucial role remains remarkably understudied in EU compliance literature. This paper argues that street-level bureaucrats at local implementing levels in Europe are bound to manoeuver between what we define as respectively a European and a national legal logic in the patchwork of EU rules on free movement, equal treatment and cross-border social rights. The two legal logics are strikingly different, yet coexisting. Nonetheless, street-level bureaucrats are left without sufficient guidance in how to prioritise and administer the rules. Consequently, discretion of unclear, core concepts in European social law such as ‘unreasonable burden’, ‘jobseeker’ and ‘worker’ is decentralised, resulting in fragmented outcome on the ground. In the limbo between a European and national logic, Union solidarity, we find, gets lost in translation.