Symptoms
Backups fail with error messages stating that the SnapAPI module is not loaded for the running kernel.
In dmesg/messages, you can find these errors from SnapAPI: "make_request_fn is NULL."
Cause
Backup agents BEFORE C21.09 release had a version of the SnapAPI kernel module (versions up to 0.7.140) that could not compile successfully on kernels 4.18.0-315 or higher (in the 4.18. series).