fwupd taking up to 200% CPU [duplicate]

Had a similar issue.

As the other answer mentioned - it is possible to determine the problem by looking at /var/log/syslog.

Within my log gnome-settings was reporting the following:

(gnome-settings-daemon:3584): dconf-CRITICAL **: unable to create file '/home/USER/.cache/dconf/user': Permission denied.

In order to fix this I ran the following command, replace USER with your username:

sudo chown USER /home/USER/.cache/dconf

I had exactly the same issue, same processes taking 100% of CPU. What worked for me was to upgrade software in my Ubuntu (16.04):

sudo apt-get update
sudo apt-get upgrade

After that I rebooted my pc and now the issue is gone.

I managed to solve it by checking syslog (/var/log/syslog). It was logging like crazy that it couldn't create the file /home/<my user>/.cache/dconf/user. When I gave this folder the correct permissions, it stopped using this much CPU.