MS Forms won't sync data to Excel in OneDrive for Business

While I don't have a resolution to your specific issue, I do have a recommendation to get around what I perceive to be consistently unstable behavior from Forms. My organization has begun creating Flows to copy Forms responses to SharePoint lists--this ensures that shenanigans with the Excel doc behind Forms never become an issue, and once in a List, Forms responses are significantly safer and much more accessible than they are in Forms (and you could still use PowerBI to report on them). At the very least, you can start seeing what new data is coming in from this method ASAP.