How many solves have you done until they start locking again? It might be that your tensions are off. More details will help. You probably don't have to redo the mod, I know someone who spent only 2 hours modding his SS 5x5 (very little plastic shaved off) and it's still damn amazing. Undermodding is not a problem, unless you somehow sculpt the pieces out of their original size and they start catching because they don't fit anymore.