So, I had the exact same problem as you.
11 disk software RAID6 setup via mdadm with an XFS partition. Disks attached via combo of mobo SATA and broadcom HBA SATA ports.
On Ubuntu 20.04.3 LTS I would get complete system freezes whenever I had high enough bandwidth writes over a short enough time period.
To rule out any other devices or network issues, I ...
This is often the result of the power saving feature in Ubuntu. You can disable this for the WiFi device by editing a file and restarting the network manager.
Open Terminal (if it's not already open)
Edit the default-wifi-powersave-on.conf file:
sudo vi /etc/NetworkManager/conf.d/default-wifi-powersave-on.conf
Note: Feel free to use any text ...
I ran into the same issue. I tried most of those complicated solutions, which didn't work. after some hours of debugging, in my case it was caused by a single SSID/network for both 5 GHz and 2.47 GHz, the Ubuntu driver just couldn't handle it properly.
You can try going to your router's IP (usually printed on the label), and changing each one of them to ...