Am I alone with this pb ?
Nope, currently the ARM boards are configured to fetch updates from https://openmediavault.github.io/packages/ (result of a discussion with @ryecoaaron a while ago) while the x64 ISOs use http://packages.openmediavault.org/public instead. Most probably there's a mismatch.
BTW: Since you're still on kernel 4.9.35 there's another problem on your installation (not receiving kernel updates any more -- see New approach for Raspberry Pi OMV images for details)