Checking into this, it looks like implementing Hw Acceleration for [Bandwidth Limit] in 4.4.0, meant that [Data Flow Monitor] could no longer be accelerated. But it might be in future.

Mmm. So they are 'robbing Peter to pay Paul'.

I can see why you would want to limit bandwidth with lower WAN speeds (FTTC), but with faster FTTP connections (as the 2927 is spec'd for) there is less need for this requirement? What is the use case to limit bandwidth on a 900Mbs FTTP connection?

I see release notes have been updated:

https://fw.draytek.com.tw/Vigor2927/Firmware/v4.4.0/DrayTek_Vigor2927_V4.4.0_01release-note.pdf

Enable Data Flow Monitor will cause Hardware Acceleration to stop working after the
firmware upgrade. Please review the DataFlow Monitor setting when meeting a
performance drop issue.