I just found this happening with Emerald after a Pokemon Box Ruby and Sapphire save. It seems the gamecube games (or I should say, games with an indirect connection as Ranch is for Wii) save back to the .sav file with some extra data or something? It saves a 129kb file instead of 128, VBA has an issue with loading it as well. I ended up opening it with the mGBA Retroarch core (had to change filename to .srm), saving again with save compression disabled in Retroarch settings (then changed it to .sav), then trying to edit again and it works perfectly. I suspect this error is similar since you mention Ranch.
I do see that you mentioned the new build will fix this issue, but I figured I'd post this in case this issue persists for some.
