If "clean workspace" is selected with a matrix build, and the workspace doesn't exist or the .git folder doesn't exist in the workspace, then it fails with:
Resetting working tree
FATAL: Command "git reset --hard" returned status code 128:
stdout:
stderr: fatal: Failed to resolve 'HEAD' as a valid ref.

For a non matrix project it works fine.

Problem is reproducible with 1.1.24 and 1.1.23 (I haven't tested earlier).