Comment 14 for bug 2018620

Another aside for those folks that may want to try to get more information in an installed system— turn on logging like so:

 1. create $XDG_CONFIG_HOME/picom.conf
 2. edit the file and include the following lines:
    log-level = "error"
    log-file = "/path/to/picom.log"

Upon restart of picom, logging will appear in the specified log file. Note that using a variable in the path such as "$XDG_CONFIG_HOME/picom.log" seems to silently fail, so make sure to use a full absolute path such as "/home/lubuntu/.config/picom.log." Note that if you want to really get a lot of info, "log-level" could be set to "debug" or "trace."

Since we're on the subject of configuring picom, there is a fork of compton-conf (the GUI tool) called picom-conf. This might be worth packaging and including in the seed:
https://github.com/redtide/picom-conf