Seems like Grincher can corrupt save data. So, do not open any mail from Grincher, leave any room you see Grincher in, and do not join any room with a 1,000 player limit called "Grincher's Happy Room". This is not a joke.
Edit: Kicking Grincher from your game does not work, they are not affected by the kick action.
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Back up your save data since it's stored locally in
%appdata%
(not a real operating system). Consider using git as well.ludusavi is a cross-platform program that automatically backs up game saves
manually:
Windows
%APPDATA%\Godot\app_userdata\webfishing_2_newver\
Steam Play (Linux)
<SteamLibrary-folder>/steamapps/compatdata/3146520/pfx