Item sold, out of stock but not showing in restock

Item sold 35 times in last 90 days, has zero stock, yet is not included in restock.

Shows up as ‘not action required’ in seller central. No flag, no status issues.

As a workaround, I have to run an inventory sorted by items in stocks to ‘catch’ those that Amazon wrongfully omitted, and add to FBA shipment ‘by hand’.

Any idea what might be causing it?