T 1076/21 (GRAIN ORIENTED ELECTRICAL STEEL/JFE Steel) vom 26.05.2023

Grounds for opposition - insufficiency of disclosure (no)
Amendment after summons - exceptional circumstances (no)
Appeal decision - remittal to the department of first instance (yes)
primary object of appeal proceedings to review decision

The burden of proof regarding the facts, arguments and evidence on the substance (which initially lies with the opponent) does not shift to the proprietor just because the patent has been revoked due to an alleged insufficient disclosure.
It is down to the patent proprietor to substantiate on appeal why that decision is wrong. The burden of proof on the substance (and in consequence the benefit of the doubt), however, is only shifted when the opposition division's assessment that the presented facts, arguments and evidence were sufficient to discharge the opponent's burden of proof turns out to be correct.
(See item 1. of the grounds)