Comment 160 for bug 272185

I think that the following command:

 sudo kill -SIGUSR1 `pidof wpa_supplicant`

Should turn on debugging until you restart.

To make it permenant then you need to change the line in the file
/usr/share/dbus-1/system-services/fi.epitest.hostap.WPASupplicant.service

from:
Exec=/sbin/wpa_supplicant -u -f /var/log/wpa_supplicant.log

to:
Exec=/sbin/wpa_supplicant -dddt -u -f /var/log/wpa_supplicant.log

Then run

 sudo killall wpa_supplicant