STM32F407 FSMC & ILI9341 – 8 bit bus width works, 16 bit doesn't
Turns out that address bits differ between 8-bit and 16-bit addressing mode. In 8-bit addressing it's mapped to bits [0-23] and in 16-bit to [1-24], so if you want to use A16 pin as CMD / DATA selection, the address of DATA transfer is 0x60010000 in 8-bit mode and 0x60020000 in 16-bit.

Source: STM32F4 Reference Manual: 36.4.1 NOR/PSRAM address mapping