This had probably been accidentally reverted in
2ebc665109887bfe95a4ad63ebe5e1d7d13c0fef ? flash_data_rom ended up on the same flash page as other unrelated data, which meant flash_flush() would've erased too much.
Also reduce nvm area to 1k and use variables to calculate area. (F042
devices only have 1kB pages vs 2k for the F072)