iphone 16p frameloss when shot 4k120 hevc with external disk

iphone 16 pro popups frameloss hint ( "!" on record button) when i shooting at 4k120 hevc with external disk.
it works fine when shooting at 4k60 hevc.
i tested the external disk r/w performance on iphone 16 pro, it's about 800MB/s read and write.
please help thx.
it works fine when shooting at 4k60 hevc.
i tested the external disk r/w performance on iphone 16 pro, it's about 800MB/s read and write.
please help thx.