Hi Pham!
Was since months that I solved this issue. Now also trying to rename .json.bk1 the 2701 games tournament isn't loaded anymore. Any idea about how to fix? Tried renaming last 2 bk and yesterday bk
EDIT: Recovered all games (using the GUI menu option) and the the crosstable, but all engines are missing.
Luckily I've managed to restore all config data and all 2600+ played games, re-adding and configurating again all engines, taking their modified names from the crosstable. The cause was Windows 11, not BSG. The tournament backup worked from the gui, but there isn't an engines + json config data backup (I've tried renaming the file) . Maybe you could add also this useful feature.