network IO issue with Ubuntu 20.04 on RPI4

[R C]

Hello,


I am running Ubuntu 20.04 on an RPI4, for data collection


I am using a USB connected wifi dongle with long range antenna,  a USB 
connection to an AD board, and a USB stick (formatted ext4) for storing 
captured data from the AD board


When I try to scp data off the USB stick to somewhere else, another 
machine, the RPI gets really slow, I do see some IO errors in syslog and 
at times the RPI even 'freezes'.

When I boot the same hardware with an SD card that has centos 7 
installed it seems to work (not lightning fast, but  consistently works).

(Centos 7 is 32bit btw.)



Ubuntu 20.04 is 64bit (which I want to keep using because the data 
logger seems to work more stable/reliable when it comes to capturing data)


Any ideas what might be causing this?  or where to start looking?


thanks,


Ron