I haven't had the bug myself but I did manange to fix a friends account after they had the bug. The easiest method to find the correct value is a fuzzy search (magnifying glass with a "?" next to it).Please help me how to find the value in GG for Magizoology , I stuck with the negative value for a long time
You use the fuzzy search to find "Dword" values. You then change your magizoology level by feeding or bonding, and then search for N=O+D (where the number that you search is the amount of xp that feeding or bonding has given you). You will know that you have the right value when only one remains.