iPhone Notes: Gmail folder notes disappeared after setting change

I just had several hundreds of notes inside my iPhone note’s app under the Gmail folder which I got since my buying this new iPhone last year. These notes are not synced to Gmail. Today I went on Settings>Apps>Notes and toggled on the “On My Phone account” toggle which creates another folder of notes called “On My Phone” (under the toggle it said explicitly said other notes won’t be affected). Right after, all the notes under the Gmail folder disappeared for an unknown reason. I assume this is a glitch because that is not the intended function. I turned the toggle back off, the notes still won’t reappear. I signed out and back into the Gmail account on the iPhone, and the notes still won’t reappear and old synced Gmail notes from before these notes I lost appeared instead. The notes I lost are not synced to Gmail nor iCloud. How can I recover the notes?