I can confirm that roundcube webmail was also broken on Debian 9 apt-get upgrade install.
roundcube-core 1.2.3+dfsg.1-4+deb9u4
roundcube-mysql 1.2.3+dfsg.1-4+deb9u4
roundcube-plugins 1.2.3+dfsg.1-4+deb9u4
To the best of my memory, it asked if you already had a database which I replied yes and I selected to keep my existing config file (no modifications to be made). After this webmail ceased working.
I meant to post this when it happened to me sometime around 5/7/20. The fix was to simply upgrade to the latest version of roundcube which for me was 1.4.4. Following that it all worked again.
You can follow the instructions by opening the forum post below.
Not sure why it broke but the fix was pretty painless.