Autossh exits without error and doesn't monitor ssh (CLD)

When I use autossh like this:
autossh -M 0 -N HOST
Autossh starts the ssh process, but then exits. It should stay on and monitor the ssh process.

When I use the same command on an Ubuntu box, it works. Same autossh version.

The problem is gone. I didn’t change anything deliberately, just installed the updates as usual.