Htop io metrs show N/A 19.07.7

Firmware is openwrt 19.07.7
htop version is 3.0.5

Add the required metrs by the following steps.
F2 -> Columns -> Set IO_RATE (or IO_RATE_READ/IO_RATE_WRITE) -> F10

You can see that several metrs related to IO are showing N/A:

The correct display should be as shown below.

And iostat looks normal.

How can I get htop to display correctly?