They just added this announcement to news:
Looks like they’re offering a transition period. Per the news:
We will still charge the FBA low-inventory-level fees incurred between April 1 and April 30, but after the end of the month, we will credit your account for all low-inventory-level fees charged during this period. Our goal is for you to see the end-to-end experience, and understand how this may affect your business so you can further update your inventory management to maintain sufficient inventory levels, drive greater sales, and avoid the fee in the future.
In typical Amazon fashion, they realized this was a big mess and implemented a “grace period” in the last minute.