Disk/Volume backup fails with:
The SnapAPI kernel module is not loaded for the kernel currently running on the system.
Acronis SnapAPI module is in charge of all Acronis software I/O operations on the hard disk. During Agent for Linux installation, SnapAPI module compiles for the kernel OS is currently running.
If there is more than 1 kernel is present and another kernel boots up next time the machine is started, dkms_installer tries to install SnapAPI on the OS start for that other kernel: SnapAPI is rebuild on each OS boot to match that kernel and to provide Agent for Backup with valid SnapAPI module.
If Agent for Linux installation prerequisites weren't met for a kernel, Agent for Linux will work only for file-level backup plan, but a backup of disk/volumes will fail.
In dkms.txt (sysinfo root folder) log, you might find something similar to:
Failed to find directory '/lib/modules/*kernel-build-name*/build' that contains the kernel sources required for the installation.
Fulfill Agent for Linux installation requirements for every kernel version in use on the machine, or forbid other kernels to load on boot (if possible).