system to hang every N second

Usually gap caused by bad sensor in lm_sensors. To solve problem you need ignore bad sensor in sensors config. Something like create file /etc/sensors.d/i8k

chip "i8k-virtual-0"
    ignore fan1

Error in sensors output

Errors like ERROR: Can't get value of subfeature temp1_input: I/O error can be caused by bad sensor in lm_sensors. To solve problem you need ignore bad sensor in sensors config. Something like create file /etc/sensors.d/iwlwifi

chip "iwlwifi-virtual-0"
    ignore temp1

The file must also be readable for all, so check file permissions, and if necessary:

chmod a+r /etc/sensors.d/iwlwifi

S.M.A.R.T. for Udisks2 disabled after reboot

You need to enable S.M.A.R.T. in BIOS

How do I rename sensors in the list?

Sensors can be renamed by modifying the file /etc/sensors3.conf or preferably in a seperate file, such as /etc/sensors.d/custom.conf (see this comment).

First you need to identify the "raw" sensor name. This is achieved by running the command sensors -u. Below is an example of the output.

>> sensors -u
nct6791-isa-0290
Adapter: ISA adapter
AUXTIN2:
  temp5_input: 26.000
  temp5_type: 4.000
  temp5_offset: 0.000

The above specifies that the sensor temp5 is labeled AUXTIN2. If we want to rename this, we write to /etc/sensors.d/custom.conf:

chip "nct6791-isa-0290"
    label temp4 "My New Label"

Note: that _input is not included in the raw sensors name.

Save the file, and Freon should update it's label automatically.

How do I hide sensors from the list?

Perform the same actions as described above, but instead of label use ignore:

chip "nct6791-isa-0290"
    ignore temp4

How do I deselect a sensor which does not exist anymore?

Sensors can be selected to display the value in the top bar. Previously selected sensors which don't exist anymore in the system appear as "⚠" in the top bar.

Since it's not possible to deselect the missing sensor, one is apparently stuck with the warning sign.

Selecting one of the available sensors re-checks the configuration and the warning sign is gone.