Ganesha version 18.104.22.168 from the nfs-ganesha repo hosted on download.ceph.com
I didn't know about that repo, and compiled ganesha myself. The developers in
the #ganesha IRC channel pointed me to
the libcephfs version.
After recompiling ganesha with a kraken libcephfs instead of a jewel version
both errors went away.
I'm sure using a compiled Version from the repo you mention would have worked
out of the box.
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