What you are seeing is called “reversion”. A plant that is showing a mutation can, at any time, start to revert back to the normal version without the mutation. This can happen normally or as a result of a change in the environment. Many people recommend more light but that isn’t always a solution. Some others recommend less light to lower the need for chlorophyll.
You can try to trim the new growth that isn’t showing the mutation. You can also cut the rhizome nearest the mutated leaves to separate it from the rest. Hopefully, new mutated leaves will grow from that separated portion.
In the end, it’s always a gamble with these mutated versions of plants.