The new memory system is not working for me either, but I found this helps. It is not perfect.
One workaround that may help is using Projects as a dedicated container for each story or world. Put detailed project instructions in there, including character notes, lore rules, formatting preferences, tone, boundaries, and anything the model needs to preserve consistently.
You can also copy your full legacy memory into a document and add it to the Project as a source file. That way, the Project has your lore, continuity, and preferences available as a dedicated reference instead of relying only on general memory summaries.
Then, if the option is available, turn off outside memory for that Project so it only relies on the Project’s own instructions and files.
It is not the same as having full legacy memory control, but it can give you a more stable workspace and reduce random outside context from bleeding into the story.