Help with memory for Asus H270F mobo ...

QVL are not all inclusive. They show examples of what works.

DDR4 2400MHz memory frequency is only supported by 7th Generation Intel processors.

DDR4 2133MHz and higher memory modules on 6th Generation Intel processors will run at the maximum transfer rate of DDR4 2133MHz.

You likely will also need to set the memory parameters in the BIOS to run at rated speeds. Enabling eXtreme Memory Profile (XMP) in BIOS will do this automatically. XMP is by default set to [Disabled].