CSV import price levels not working for some products

We regularly generate a CSV file of item prices for importing into MYOB AccountRight. This includes making use of the pricing levels fields for custom pricing (e.g. "Price Level A, Qty Break 1"). I've uploaded a sample CSV import file with the pricing levels in it.

I do not get any errors/warnings when running the import, but when I manually check the products, some do NOT have updated pricing level values - MYOB just seems to refuse to update this data. However, if I manually add/update a single pricing level for a product and then run the CSV import, all pricing levels are updated! I've exported all item data before and after manually updating a product, but there a no extra flag/option that changes.

I've tried out a heap of different import options and combinations of fields (including ignoring the Level A price and just relying on Selling Price and Level B pricing). I'm not sure if this is something that only happened recently or not as we update prices in bulk every month or two normally.

I really need to have reliable CSV pricing imports happening again, so any advice is appreciated.