Earlier this week, I broke my Debian install. I was running Debian Sid (testing) and ran an update and lost my GUI environments. Sid is a testing version; if you run a testing version, you have to expect stuff to happen. Plus I had been having quirky stuff happen for quite some time, so I suspect the issue was mine and not Debian’s.
I was too lazy to troubleshoot the problem, so last night I reinstalled Debian Stretch. Since I had my home directory on a separate partition, all my personal files and settings were preserved, as I simply reinstalled the OS to the root partition. Consequently, once I reinstalled and started programs, they behaved as previously configured.