Courts must generally comply with their so-called duty to provide information (Section 139 ZPO) before the oral hearing! – BGH ruling from 11.4.2018 (case no. VII ZR 177/17)
Unfortunately, it is common practice in civil proceedings for the courts to only issue instructions to the parties during the oral hearing. The BGH dealt with the consequences of this practice in a practice-relevant decision dated 11.4.2018 (case no. VII ZR 177/17).