Functional workaround found in a different discussion.
The current workaround answer for new (i.e. no rollback kernel option) systems is to:
apt install -y linux-modules-extra-azure
Apparently the problem is that they moved the location of the CIFS driver from fs/cifs/ to fs/smb/client/, but didn't update the include file for building the base modules package to include the new path.
https://www.mail-archive.com/kernel-packages@lists.launchpad.net/msg514627.html