The U-Block chips only output COG when the speed is above a certain threshold. I have a Chinese knockoff based M8030-KT. It doesn't output COG until it reaches 0.1 kn.
The chips, series 7 and 8 are highly configurable using U-Center software
sentences output (so it doesn't spam GSA and GSV sentences)
GPS vs GPS + GLONASS, affects NMEA talker ID used. I set mine to GPS only so that it only outputs $GP, not $GN and $GP
The above are just some the settings available.
Make sure the U-Center version matches the chip. In my case, v20.10.