Migration from older versions to 0.31.4 and beyond
0.31.4 is a breaking release. It is not compatible with previous versions of Raspotify. Special care needs to be taken when updating from updating from =< 0.31.3 to 0.31.4+ or Raspotify may end up in a broken state.
Beginning with version 0.31.4 Raspotify will take advantage of librespot's ability to parse environment variables. The most obvious user facing change is that Raspotify's configuration file will change places (from /etc/default/raspotify to /etc/raspotify/conf) and change formats. Where as before the sections were basically "arg dumpsters" that you could put pretty much anything into, the new conf format will be closer to a traditional configuration file that sets environment variables that map 1 to 1 to librespot's options and flags.
After you take note of your old config values and/or back your old config to a new location you should run sudo apt purge raspotify to completely remove purge Raspotify and then reinstall with sudo apt install raspotify.
You can than migrate your settings to the new config.
/etc/raspotify/conf will contain a non-exhaustive list of librespot options and flags. If you don't see the option or flag that you normally use you can add it and so long as it's valid it will work. To avoid name collisions environment variables must be prepended with LIBRESPOT_, so option/flag foo-bar becomes LIBRESPOT_FOO_BAR. If you look at the rest of /etc/raspotify/conf it should not be difficult to understand.