Very slow boot time with non routed subnet


I’m encountering a very strange behavior when adding a non routed subnet on my machines.
For example, let’s say I want to add a private, non routed network shared by every machines for things like Ceph cluster network, it can be easily done through MaaS UI and it is effectively applied to the deployed machine.
But, when starting, the machine hangs for nearly 2mn when starting systemd-networkd-wait-online.service until it gets a timeout.

When completely started, this network is up and everything is fine but it makes boot times very long for no reason.

Does anybody has any idea why this is so long and why this service fails ?
I tried it with both Ubuntu 18.04 and 20.04 with same behavior.

Best regards