It appears the issue in #23909 was reintroduced at some point. This bug is again present in Foreman 3.5.3. It looks like the same underlying confusion of the "key" versus "id" field in fog_extensions/vsphere/server.rb is to blame. In that file, changing

vm_network = all_networks.detect { |network| nic_attrs['network'] && [network[:name], network[:id]].compact.include?(nic_attrs['network']) }

to

vm_network = all_networks.detect { |network| nic_attrs['network'] && [network[:name], network[:key]].compact.include?(nic_attrs['network']) }

resolves the problem. The symptoms & conditions of this error are identical to the previous ticket.